Codec issue?

Hi! I’m new to this forum.
I would like to submit this issue.
I have a Freepbx installation running on raspberry. The freepbx point to the telco router which offer SIP connectivity, as well as 2 analog ports and DECT. On freepbx I have configure a CISCO phone, a CISCO ATA (2 ports analog) and some softphones running on PCs.
Everything works fine (incoming, outgoing and internal calls on the pbx).
The issue that I have is that: when an external call arrives, every device is ringing. If I pick up the call on one device point to freepbx everything is OK. If I pick up the call on an analog phone connected directly to the router, the call is established, but I have no audio in both directions.
If I switch off freepbx, the calls via the router are OK.
Is this a codec issue?