I'm using OH 3.1.0 M3 build on Ubuntu 20.04 LTS 64bit on Raspberry Pi 4 (8GB RAM) and Azul Embedded Java 64Bit. With M2 sumSince calculations ware working well like "SM_PV_EigenverbrauchGesamt.postUpdate(SM_PV_EigenverbrauchTag.sumSince(parse("2021-01-01T00:00+01:00[Europe/Vienna]")) as Number". Since OH3 the item name is written as Tag in the Influx DB (version 1.8). Caluclations (with values that have a tag or not) are working in M2. With M3 the calculations only sum up the values that have the Item name stored as tag in InfluxDB. I do not have any tags configured in my OH Persitence config. Also charts do not show the values (which are not used in the sumSince calculation).
Log says: 2021-04-04 15:26:18.493 [INFO ] [b.internal.InfluxDBStateConvertUtils] - Could not find item 'null' in registry