Problem with call recording and g729 codec

Hello Everyone,
We are using Asterisk 13.8.2 and one of our CC has problem with voice recording via MixMonitoring (both: function and app). One of our provider is using g729 codec (only this one, we can not change it), so we bought licence for 60 channels and everything looks good, voice quality during the call is fine, but we have trouble with voice recording. We tried almost every format (wav, WAV, gsm…). The speech (in the record) is degraded with “occasional crackling sound” but ONLY for outgoing calls and ONLY for our operators. It is strange for me, because like i said call quality during the call is fine. It is hard to understand what our operators are saying from the records.

I spent almost 3 weeks of testing, and i found:

  1. We replaced MixMonitor() with Monitor() and -m options, sound quality is fine BUT we have problem with synchronization between channels.
  2. spy function is also degraded, in the same way like records from MixMonitor.
  3. problem is only for outgoing calls and only for our operators (the voice from caller side-our OP- is degraded in the record) and only for the provider with the g729 codec.
  4. the problem start with replacing our old PBX (asterisk v1.4) with the new one (asterisk 13.8.2). It works fine in the old PBX an di have acces there, so i can show every setting.
  5. no errors or warnings in CLI

To be honest, i dont know what to do now. Where to start, we are using very simple dialplan as MixMonitor and then Dial().
i will show any logs as you want…

Thank you