Looks like it’s not uncommon for the MK1310 to have issues with Chirpstack:
Doesn’t look like your exact issue as this guy atleast gets join/accepts but something to be aware of.
As for V4 if you have a spare server to try it (so then you don’t need to delete your current one incase the migration fails), then there would be no harm in giving it a shot. The migration itself really is not hard (although I have not done it before): v3 to v4 migration - ChirpStack open-source LoRaWAN® Network Server documentation, and then you need to make sure you do the v4.7 redis → postgres migration as well (a single command): [release] ChirpStack v4.7