Again, I’m not telling anyone NOT to use pjsip. If it works for your situation, that’s great. But, lots of people are reporting that it doesn’t work for their situation. The usual response seems to be to forward all your ports, which is terrible security advice, and is generally not necessary.
Reports of pjsip issues are all over the forum. If you can’t accept these, then I don’t know what to tell you. Again, here’s one from a few days ago, that I experienced MYSELF as well: