We just converted a bunch of phones to PJSIP to see if it works well and we ran into an issue during the middle of the day when the server is being used heavily. When a voicemail is left on an extension it will appear then disappear on the phone but it seems to only happen when MWI subscription type is set to auto.
So a voicemail will appear on the phone and show you have a new voicemail. After waiting a little bit the notification will disappear. After a while it reappears and repeats this infinitely. Using a BLF key with *982314 correctly shows if there is a voicemail or not. This only happens when the server is being heavily used and does not occur during slow periods.
Switching from Auto to either Unsolicited or Solicited solves the issue.
Has anyone else had this issue? Any idea if this would originate from Freepbx or Asterisk?
Edit: Which one of those two options should I pick for most Yealink/Grandstream/Polycom phones?