S20 Allowed Country IP issue

I have a number or S20 installed, but one is now causing an unusual issue. When the allowed country for the US and Canada is enabled (my area), the INVITE from the provider will hit the S20 and then go to the ring group as normal. An extension from the ring group will answer and the 200OK will have the SDP info from the phone, but the PBX does not open an RTP port back to the phone despite the ACK to the OK. The local IP LAN segment is The provider is Telnyx and using the US domain. 

I removed the PBX from service and brought it back to the office and changed the external NAT IP and added in my local LAN segment of and repeated the test and I had no issue in getting two-way audio from either provider. 

I returned the device back to the original location and again changed the external NAT IP and removed my office LAN segment. I left both providers installed. Calling to/from Telnyx would always result in the PBX not opening up an RTP port. The extension would never hear the other end. 

Using SIPTRUNK.com, there was no issue in either making or taking calls with two-way audio. 

I checked 3 other S20 and all were set the same way, but only the one I am reporting about is the one with the issue. Finally, at the end of my rope, I recalled that I had reported that ping was impacted by the same function on an earlier F/W version and had worked with Wayne to confirm. The solution was to disable it when ping was needed pending a new firmware release.

I disabled the Allowed country and audio is now working with both providers. I should mention that I also re-enabled the function and can repeat the results where the PBX will pass the audio to the phones using SIPTRUNK and the other (Telnyx), Telnyx it would not. The audio (RTP) from both is reaching the PBX without issue. 

I also added an explicit rule to the firewall to allow the local LAN segment despite there already being one installed from Yeastar. IT made no difference. 

It is not clear to me how the allowed country function has no issue allowing both providers to work on my LAN segment, but then only allowing 1 provider to work correctly on the other, while stopping the RTP (only) to the extension when on a different. 

The 3 others I checked are all using the same LAN segment, with Telnyx as a provider and with the allowed country function enabled and none have this issue. 

Due to the current sPBX shortage I have nothing to replace it with and it is working at the moment with the function disabled. It is a very small install with only 5 user extensions. 

The PBX is running the same firmware as the other as well -


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