Darn it Andrew I’ve got a POTS gateway that doesn’t work with pjsip, now I’ll have to go through the bother of setting up a test server and filing a proper bug report… 
Remember he said he’s paying for hosting. If his hosting provider is a real virtual provider it couldn’t be ram, since at any given instant his virtual server could be running on a different physical server (or several physical servers) Of course, if his virtual hoster is a garage operation with a stack of a couple hundred 1U physical servers that could be the case but then why wouldn’t the other virtual servers on the same physical server he is on be having trouble? But in either instance that wouldn’t be his problem it would be his hoster’s problem.
But setting up a physical server would be a great next troubleshooting step, that allows for subtracting the virtualization as a potential source of trouble.