Leveling up twice with free XP

[Excaliburp]

I have this problem where I gain enough XP to level up, assign my skill points and perks, then go back to the game, only to suddenly have my XP regress enough to lose a level and immediately gain enough XP to level up again, only I keep the skills and perks I gained the last time.

 

To give an example of what happens, I have 4998 XP now, I kill a molerat, get 5 XP and end up with 5003 XP, which levels me up to level 6. I assign everything, then 10 seconds later, my XP regresses to 3577 without my knowledge, then *ding* and I immediately gain 1423 XP to level up up to level 6 again. Skills and perks from my previous level up to 6 is retained. I can confirm that I wasn't doing anything after killing the molerat, just standing around.

 

I can reproduce this "bug" most of the time.

 

My mod list includes FOOK, XFO, Enclave Commander, MMMF3, and some miscellaneous mods I don't think will cause this. I used to have UPP on, but turned it off when I started getting this problem, and that solved it that one time, but it is happening again now. My current character doesn't have any of the UPP perks, by the way.