I noticed this happening with one of my accounts, where I am loading into it to either support another player, or by myself. The change was for the worse on this account, and I’ve never been able to restore the number of tokens or ranking I used to have. Let us say you previously had gun damage at 15%. Then you notice it has gone down to 5%. I theorize that this can happen due to multiple accounts interacting, where the account that got the hammer is the second or third to load into the game and it is being done on the in-game page, not the Main Menu.
The only revenge I can suggest is to run your UVHM character in NVHM or TVHM and choosing easy activities like Fink’s Slaughterhouse. Simple cheesy activities are the way to go, and since BAR points are not based on XP but just killing or collecting, this is the only way to get the percentages back to where they should be. Even creating new characters (say level 30) will add to ranking if you stick with normal activities.