Vassal pass-up XP question and possible issue

As old players returned during March, many of them return to find their patron inactive. I have been helping a return player quite a bit and he wanted to sub to me as to not waste the pass-up XP. When he subbed, I noticed the allegiance panel showed that he'd already passed 1+ billion XP to me right when he subbed. I thought that was strange and ignored it. Now, the XP he's passed up to me has hit the login cap of 4+ billion XP and hasn't moved. I'm thinking the game thinks he's still subbed to his old patron and has stopped passing up XP.

Is anyone else seeing this issue? Does anyone have any suggestions on a fix/work-around?

Thanks in advance.