Several 8831s at a site report one way audio periodically. The users dial into an external, third party conferencing service. Once in a while, everyone else can't hear the users on the 8831. They have to hang up and dial in again. The firmware is sip8831.10-3-1SR4-2-NA, CUCM version 10.5.1. The problem will, of course, disapear for a week or so and come back. There are 10 total 8831s at the site, but only 4 complain. There are around 100 8831 phones in the whole company and only one phone in one other site has complained of the exact thing. Always the other callers cannot hear the users on the 8831. They say, when they call the conference service from their desk phones 8841s, there is no problem.
Anything else to look at?