I’ve been dealing with this issue for several months.
Free PBX 16 running Asterisk 20 (also occurred on v18)
Endpoints are Polycom VVX 410s
Using PJSIP w/ TLS and SRTP
SRTP Replay Protection: No
When a phone places a call on hold, we will occasionally see the following errors in the PBX logs:
VERBOSE[19720][C-00000a1d] res_srtp.c: SRTCP unprotect failed on SSRC 1875483051 because of authentication failure
The phone logs show:
0424113855|srtp |4|00|srtp: srtp_unprotect_rtcp: error: 10 - failed seq number 1 for replays, SSRC=0xdbba98d
0424113900|srtp |4|00|srtp: srtp_unprotect_rtcp: error: 10 - failed seq number 2 for replays, SSRC=0xdbba98d
0424113905|srtp |4|00|srtp: srtp_unprotect_rtcp: error: 10 - failed seq number 3 for replays, SSRC=0xdbba98d
0424113910|srtp |4|00|srtp: srtp_unprotect_rtcp: error: 10 - failed seq number 4 for replays, SSRC=0xdbba98d
0424113914|srtp |4|00|srtp: srtp_unprotect: auth failure - seq=0x8f91, ROC=1
This happened a lot more often before we disabled SRTP Relay Protection, but the issue still occurs.