FCP X synchronization stopped working

 [Loaded] com.macpaw.CleanMyMac3.Agent.plist (MacPaw Inc. - installed 2023-12-13)
    Executable: /Library/PrivilegedHelperTools/com.macpaw.CleanMyMac3.Agent

and

[Loaded] com.google.GoogleUpdater.wake.plist (Google LLC - installed 2024-06-16)
    Command: ~/Library/Application Support/Google/GoogleUpdater/Current/GoogleUpdater.app/Contents/MacOS/GoogleUpdater --wake-all --enable-logging --vmodule=*/components/update_client/*=2,*/chrome/updater/*=2

CleanMyMac is known to break FCP. It's possible that simply uninstalling it might help, but others will likely chime in that a clean reinstall of the macOS is necessary.

Chrome's background processes that are always running are also known to break FCP. Follow the instructions at https://chromeisbad.com for info on how to completely remove all the cruft Google installs. Simply trashing Chrome.app is not enough.

Internet Plug-ins:
  Silverlight: 5.1.50901.0 (? - installed 2018-06-09)

Having Silverlight installed indicates that you've been upgrading the OS across many versions. This can lead to carrying forward old software that is incompatible with the current OS. This would be another reason to do a reformat and clean install of the OS, then reinstalling software from the AppStore and 3rd party developers.

it didn't work with the exact same video and audio files that previously had successfully been used to synchronize.

Can I share previously synced videos and audio sources?

Upload to WeTransfer →Send to yourself →Post the link you obtained.

●https://wetransfer.com/

As usual, whenever the application misbehaves, deleting preferences may help. To delete preferences, hold down command and option while starting the application and click Delete Custom Settings. The application will start with default settings and open an “Untitled” library. Adjust the settings, reopen the library you were working, and see how it works now.

For comparison, try making a multicam clip instead. Do they synchronize correctly if you make a multicam?

If they do, then you can use it as a temporary workaround.

What version of FCP and of macOS?

Any recent changes to either?

Do you have Chrome?

I have just done a little test, and the synchronization worked perfectly, also using 10.8 on Sonoma 14.5.

Perhaps there is some other software issue.

You could try deletinng FCP and downloading a new copy from the App Store, but in this case it seems unlikely to help.

To see if there are other potential issues: Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

First make sure each group of audio and video clips from the same camera or recorder are labeled in the video inspector (CMD+4 toggles) under "Camera Name." IOW select all video clips from a given camera in the Event Browser, and assign a camera name in the Inspector. Do the same for audio-only clips from a given recorder.

Then in the Event Browser, skim through each clip and place a marker (M key) on very roughly the same visual or audio point. It need not be exact. This will constrain the audio waveform search to a tighter range and increase the chance of a successful sync. IOW in the Create Multicam Clip dialog you can select *both* "Use Audio for Synchronization" *and* Angle Synchronization: First Marker on the Angle.

Then try to create the multicam clip and see if it syncs.

In the Sync dialog, is "Use audio for synchronization" checked?

Would it be possible to share the files as LocaAlicia suggested? It might help to see where the problem might be.

CleanMyMac is really dangerous, I'd make sure to remove that 100 percent from your system!