MS Teams no RTP with some Costumers

I am running into an issue with our new MS Teams Direct Route. With some costumer, we are not able to get an RTP stream. Each time the call can be answered, but there is no audio. Our Provider told me, there is a problem in the Microsoft site (left) and sends me the trace below. But I am not sure about this. I see the left site is answering the INVITE but the SBC in the middle does not send the trying to the right site? So, in my opinion, there is a Problem with the AudioCodes SBC and not with on the MS Teams site (SBC is hosted by the provider). Or am I wrong? Thanks for help! 🙂