I wonder if an experience value isn't getting rounded correctly? Sounds like a mod issue, not something I have encountered.
Possible, but I've encountered this issue for many builds and I believe previous tests without any mods (or changes to base files) repro'd this problem. However; it's been so long I can't confirm. Will do a test profile here soon and see what I can find out.
In terms of XP-modifying mods, I use KMC Server Value Modifier and previously used the Ereshkigal AkiConfiugurator long ago. Occurred with both of those before.