So, hello everyone!
I have got the same issues here. I upgraded my FreePBX Distro to V13 with Asterisk 13.5 - all updates are installed.
In the past, I was using chan_sip to connect to my endpoints and trunks and everything was fine. For testing purposes, I changed some extensions to use pjsip. And that's when all got odd. It's the same as described here. Internal calls between to pjsip extensions using G722 work just fine - but when it gets to playback of internal audio files like announcements, there is just silence. I've tested with different extensions and different endpoints. My Yealink T38G, my Grandstream GXV3175v2 and my Siemens Gigaset VoIP DECT Phone. All the same. All have worked properly with chan_sip, but they don't do with chan_pjsip - as long as you use G722 as voice codec. Only my Aastra 6755i seemed working as it should.
I then figured out a mysterious behavior: In the phone configs, I had set the phones to may use multiple voice codecs. G722, alaw and gsm (as I live in Germany), while the G722 codec came in the first place, as ist should be prefered. I removed all codecs except the G722 in the phone configuration. Believe it or not, that did it. All phones now were playing the audio files.
Of course this is not a solution, because I still want the phones to be able to use a branch of codecs, as they did, when using chan_sip. For me, there are still issues, that make me return to chan_sip. That's because, my trunks use chan_sip with alaw as codec, and with pjsip endpoints external calls only ring 10 seconds and then break down - but are displayed and handled as answered. I think, this might also have something to do with the codec or the transcoding.
So, if you ask me: I don't think we have an FreePBX related issue here. It also isn't phone related, because ist happens on multiple endpoints. In deed, only my Aastra Phones seem to have no problems even when multiple codecs are selected. What we have here seems to be a problem with the chan_pjsip driver.
Oh, by the way: I followed your tip, Rob. Factory reset and just registering the phones didn't change anything.
Perhaps my "encounters" help to solve the problem.
Kind regards from Germany
Andy