This! I'm obsessive about my hotbars and this has been driving me nuts.
I tried the 'custom' tab in hopes that it would be the solution, but I didn't even bother once I saw that there are no numbers or hotkeys associated with those slots.
Very disappointed that the hotfix didn't fix this issue (I read through the notes and then tried it out, still the same). Larian, please let us choose where we want spells, again (I put a cantrip or whatever my most-used attack is on 1 for each character, makes fights go so much more smoothly).
(By the way- this isn't just for spells. I moved Astarion's rogue bonus actions over to the common bonus actions and the game moved them back after I loaded that save.

)