I've had MM info get corrupted before from the game crashing while MM was doing its thing. (Game crash wasn't due to MM. I blame ZOS... and the fact that I use over 200 addons.)
Maybe that's what happened in your case?
If you don't already use it, I highly recommend
ESO Saved Variables Auto Backup. It has saved my butt too many times to count. If you had been using that, you could have reverted your LibHistoire and/or LibGuildStore to a slightly older file and perhaps fixed the issue.
I'm sorry I can't assist further. I do hope you figure it out.