HT813 doesn't always answer FXO


Hi Guys

re-posting in here as original was in PBX and think this is more relevant.

Hoping for some help here.

I have 3 HT813 with the FXO ports connected to analogue lines on an old PABX.

All three intermittently don’t answer incoming calls even though they ring for 40 seconds plus, one only answers 50% of the time.

Problem seems worse under heavy load.

Any ideas.

Thanks in advance