If some are working and others aren't, maybe they've got some things unchecked in the sheet settings. On the character sheet, they can look at the settings tab (the one that looks like a little cog between "Character" and "All"), and there are a few checkboxes which allow you to choose HP recovered on a long rest as well as how many Hit Dice are recovered on a long and short rest. Maybe that's the problem? EDIT: After testing, it looks like there should still be a chat notification that a rest was taken, even if nothing was recovered, so this is likely not the issue.
