Recent VOIP disconnections

[keeka]

Some time after upgrading to 25.1.9, I seem to be seeing VOIP disconnections when call duration exceeds approx 900 seconds.
Prior to this all calls, including some lasting over an hour, were uninterrupted.
I cannot accurately correlate the problem with the upgrade as there were no calls of sufficient duration for 2 weeks.

Were there any changes in 25.1.9 that might be related?