Yeah -- same problem with the hotbar -- just the Z, X , C, and V, and everything else blank. I disabled "Better Hotbar 2" and things started working again (albeit with less hotbar space), despite dire warnings in pop-ups that things might break when I loaded my save. I don't have many mods installed (just 6 actually) so it was easy to find the culprit. I kept ImpUI installed & active, along with other "Better Container" etc. mods, and that was fine.

The only problem is that the dividers in the hotbar seem to be irredeemably messed up (until if/when the mod is fixed & I can reactivate it), but that's not a blocker as I can just click on the tabs to see what I need in the meantime. I miss the wider hotbars though...