Extension keeps reregistering

I’m having a problem with an extension registering again and again.
1.- The log file does not record a disconnect.
2.- Every two minutes on the second it registers again
3.- During this cycle there is a time when the phone does not ring during an incoming call.
4.- Extensions take turns with this happening, one at a time.
5.- I was never cut off during a call.

I upgraded to the latest Freepbx, but had similar problems before. The phones are Polycomm 335.


Can you please show the asterisk logs?

I had posted earlier, and I found the post. I followed the recommendations and I downgraded one step - to 11.19 I believe - and now everything is stable. There was nothing in the log files that gave me any clue.