Hi,
I used Upload to SD card, then printed from that - I get these kinds of messages in the log
2020-09-25 14:43:37,492 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): dropping command
2020-09-25 14:43:37,493 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:G1, cmd:G1 X1.482 Y-9.400 E1.5032

The extruder sounds like it's grinding or skipping steps or something. I also see this:
2020-09-25 16:23:46,385 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M119 Received. | Endstop: X-max:0 Y-max:0 Z-max:0 | MachineStatus: READY | MoveMode: READY | Status: S:1 L:0 J:0 F:0 | ok |
2020-09-25 16:23:46,387 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:46,389 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:46,391 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M27 Received. | SD printing byte 0/1000 | ok |
2020-09-25 16:23:46,392 - octoprint.plugins.flashforge - DEBUG - buffering: CMD M27 Received.
2020-09-25 16:23:46,394 - octoprint.plugins.flashforge - DEBUG - buffering: Not SD printing
2020-09-25 16:23:46,395 - octoprint.plugins.flashforge - DEBUG - buffering: ok
2020-09-25 16:23:46,398 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:46,400 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:46,402 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:46,403 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:47,364 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:M27, cmd:M27
2020-09-25 16:23:47,364 - octoprint.plugins.flashforge - DEBUG - is_sd_printing()
2020-09-25 16:23:47,366 - octoprint.plugins.flashforge - DEBUG - write() called by thread comm.sending_thread
2020-09-25 16:23:47,367 - octoprint.plugins.flashforge - DEBUG - write() M119
~M27
2020-09-25 16:23:47,376 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M119 Received. | Endstop: X-max:0 Y-max:0 Z-max:0 | MachineStatus: READY | MoveMode: READY | Status: S:1 L:0 J:0 F:0 | ok |
2020-09-25 16:23:47,377 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:47,380 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:47,382 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M27 Received. | SD printing byte 0/1000 | ok |
2020-09-25 16:23:47,383 - octoprint.plugins.flashforge - DEBUG - buffering: CMD M27 Received.
2020-09-25 16:23:47,384 - octoprint.plugins.flashforge - DEBUG - buffering: Not SD printing
2020-09-25 16:23:47,384 - octoprint.plugins.flashforge - DEBUG - buffering: ok
2020-09-25 16:23:47,386 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:47,387 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:47,388 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:47,388 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:48,359 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:M105, cmd:M105
2020-09-25 16:23:48,360 - octoprint.plugins.flashforge - DEBUG - is_sd_printing()
2020-09-25 16:23:48,363 - octoprint.plugins.flashforge - DEBUG - write() called by thread comm.sending_thread
2020-09-25 16:23:48,364 - octoprint.plugins.flashforge - DEBUG - write() M105
2020-09-25 16:23:48,367 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:M27, cmd:M27
2020-09-25 16:23:48,369 - octoprint.plugins.flashforge - DEBUG - is_sd_printing()
2020-09-25 16:23:48,374 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M105 Received. | T0:28 /0 B:0/0 | ok |
2020-09-25 16:23:48,374 - octoprint.plugins.flashforge - DEBUG - buffering: CMD M105 Received.
2020-09-25 16:23:48,376 - octoprint.plugins.flashforge - DEBUG - buffering: T0:28 /0 B:0/0
2020-09-25 16:23:48,377 - octoprint.plugins.flashforge - DEBUG - buffering: ok
2020-09-25 16:23:48,380 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,383 - octoprint.util.comm - INFO - Externally triggered heatup detected
2020-09-25 16:23:48,395 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,397 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,399 - octoprint.plugins.flashforge - DEBUG - write() called by thread comm.sending_thread
2020-09-25 16:23:48,400 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:48,401 - octoprint.plugins.flashforge - DEBUG - write() M119
~M27
2020-09-25 16:23:48,411 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M119 Received. | Endstop: X-max:0 Y-max:0 Z-max:0 | MachineStatus: READY | MoveMode: READY | Status: S:1 L:0 J:0 F:0 | ok |
2020-09-25 16:23:48,412 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,414 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:48,417 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M27 Received. | SD printing byte 0/1000 | ok |
2020-09-25 16:23:48,418 - octoprint.plugins.flashforge - DEBUG - buffering: CMD M27 Received.
2020-09-25 16:23:48,420 - octoprint.plugins.flashforge - DEBUG - buffering: Not SD printing
2020-09-25 16:23:48,421 - octoprint.plugins.flashforge - DEBUG - buffering: ok
2020-09-25 16:23:48,423 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,426 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,429 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:48,430 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:49,371 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:M27, cmd:M27
2020-09-25 16:23:49,373 - octoprint.plugins.flashforge - DEBUG - is_sd_printing()
2020-09-25 16:23:49,376 - octoprint.plugins.flashforge - DEBUG - write() called by thread comm.sending_thread
2020-09-25 16:23:49,378 - octoprint.plugins.flashforge - DEBUG - write() M119
~M27
2020-09-25 16:23:49,386 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M119 Received. | Endstop: X-max:0 Y-max:0 Z-max:0 | MachineStatus: READY | MoveMode: READY | Status: S:1 L:0 J:0 F:0 | ok |
2020-09-25 16:23:49,388 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:49,389 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:49,392 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M27 Received. | SD printing byte 0/1000 | ok |
2020-09-25 16:23:49,393 - octoprint.plugins.flashforge - DEBUG - buffering: CMD M27 Received.
2020-09-25 16:23:49,394 - octoprint.plugins.flashforge - DEBUG - buffering: Not SD printing
2020-09-25 16:23:49,396 - octoprint.plugins.flashforge - DEBUG - buffering: ok
2020-09-25 16:23:49,402 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:49,408 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:49,411 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:49,413 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:50,375 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:M27, cmd:M27
2020-09-25 16:23:50,376 - octoprint.plugins.flashforge - DEBUG - is_sd_printing()
2020-09-25 16:23:50,378 - octoprint.plugins.flashforge - DEBUG - write() called by thread comm.sending_thread
2020-09-25 16:23:50,380 - octoprint.plugins.flashforge - DEBUG - write() M119
~M27
2020-09-25 16:23:50,389 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M119 Received. | Endstop: X-max:0 Y-max:0 Z-max:0 | MachineStatus: READY | MoveMode: READY | Status: S:1 L:0 J:0 F:0 | ok |
2020-09-25 16:23:50,390 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:50,392 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:50,395 - octoprint.plugins.flashforge - DEBUG - readraw() returns: CMD M27 Received. | SD printing byte 0/1000 | ok |
2020-09-25 16:23:50,396 - octoprint.plugins.flashforge - DEBUG - buffering: CMD M27 Received.
2020-09-25 16:23:50,398 - octoprint.plugins.flashforge - DEBUG - buffering: Not SD printing
2020-09-25 16:23:50,399 - octoprint.plugins.flashforge - DEBUG - buffering: ok
2020-09-25 16:23:50,402 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:50,404 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:50,407 - octoprint.plugins.flashforge - DEBUG - readline() called by thread comm._monitor
2020-09-25 16:23:50,407 - octoprint.plugins.flashforge - DEBUG - readraw() called by thread: comm._monitor, timeout: 2000
2020-09-25 16:23:51,378 - octoprint.plugins.flashforge - DEBUG - rewrite_gcode(): gcode:M27, cmd:M27
2020-09-25 16:23:51,379 - octoprint.plugins.flashforge - DEBUG - is_sd_printing()
2020-09-25 16:23:51,382 - octoprint.plugins.flashforge - DEBUG - write() called by thread comm.sending_thread
2020-09-25 16:23:51,387 - octoprint.plugins.flashforge - DEBUG - write() M119

I use Simplify 3D to slice, and the gcode files directly out of that always work if I load them via a usb flash drive at the unit directly.