Greetings Jehan, We've worked together before. I'm with Comrex and we build the hardware this user is trying to connect to. I've tested this and might be able to add something. As Patrick mentions, the first call works fine. Subsequent calls negotiate properly and begin the RTP sessions, but after about one second the outbound RTP from Linphone starts to fall apart. It also decodes the inbound RTP for about one second before silence, although the inbound RTP looks OK. This is true of at least Opus and G.722 calls. This is Linphone 3.16.1 on an iPhone 6 on iOS 10.2.1. I don't think it has anything to do with the Comrex gear.
If Patrick's capture doesn't enlighten I can generate some here as well.