I have tried many different variants of the following scenario:
1) Go to my residence as level 6 with enough xp to make level 7
2) confirm that I want to do a long rest even though I did one already for the current day and accept that I will have to wait
3) I hover the mouse over a "level up" button and watch it light up when I click. Here's where things go wrong. Sometimes the screen refreshes with the character going up, and sometimes it doesn't. I have had it do three characters and start ignoring me on the fourth, and I have had it only raise my wizard, which is in slot 4. I have a shadowcaster, a spell blade, a cleric and a wizard shock arcanist. It seems to get lost most often on the spell blade, and I have no idea why.
4) I click on the remaining "level up" buttons until I get bored. Nothing novel or interesting happens.
5) I exit the long rest with everything done for up to three characters.
6) rest and repeat steps 4-6, or reload and try the characters in a different order doing steps