Bugs, or unfinished coding, when players take long rests or level up?

Last night I told my table to level up. This did not reset their HP or class features. Why wouldn't a level up automatically trigger a reset of HP and features? Because then I went through each sheet and tried using a Long Rest to reset everything, which fixed HP but not class features; I had to manually reset everything else. Is this a really big bug in DDB or coding that's never been addressed?

It's neither a bug nor "unfinished coding"; per the actual rules of D&D, gaining a level does grant any healing or reset any features that require resting to reset. You need to actually take a rest to do that.