There are always some issues with every point-x update, but I can't find any specific reports of what you describe.
Assuming you did the usual hard shutdown/restart, you could try..
- blowing out the Preferences
- re-installing Logic
If you zipped/saved the previous version of Logic before you updated (as recommended by Apple),
you could revert to that and see if that still works.
Aside from that, here are a couple of troubleshooting considerations..
- Did you change/update anything else when you updated Logic?
- Is this problem fairly consistent (frequently happens) or intermittent?
- If it's intermittent, what's common about the times you encounter it (particular song, Instrument, etc)?
- Which Instrument(s) are you trying to play when it happens?
- Do you see level in the meter(s) but don't hear the audio, or no level in the meter(s)?
- Did you check the controller/USB connections, or test with a different controller