Bonjour Nick:
Is Asterisk running? If not can you restart or does it fail to start? You can start Asterisk with verbose flags with:
sudo -u asterisk asterisk -cvvv
Perhaps you will get a clue if it throws some errors as the startup fails. My guess is that there is something in one of the pjsip conf files that Asterisk doesn’t like, but I don’t know how that would be possible. For what it’s worth, I use pjsip on most of my systems without ever having seen this happen.