Good news and bad news. Good news is, I may have figured out how to reproduce the issue that's causing a certain people's sheets to fail updating level/hitdice and crashing. Bad news is it may be related to one of these issues: A. An old issue that caused a massive amount of d0 hitdice to be created, probably throwing an error into the hitdice calculation B. A conversion issue from older editions to a more recent version , although which one, I cannot say. It seems like the bug *only* affects sheets from older versions of the sheet (maybe as far back as 15.5.0, but I have a really good feeling it concerns one of the breaking change for blank fields roll20 pushed a couple months ago?) Right now, I'm reproducing the problem somewhat reliably with campaigns that have previously used an older version of the sheet at some point in their lifetime. I'll post an issue if I can CONFIRM that my suspicious for these conditions are correct. Once I do, I'll send a suspect sheet towards the test campaign to confirm the issue. Edit: @Kryx Just wondering, but did the change to the empty fields affect how fields are re-populated? Like, if I, say, deleted all of the attributes relating to hitdice (from attributes and abilities), does it force a recalculation? One thing I noticed is deleting the hitdice count from attributes sometimes just deletes the field, but it never comes back. I'm not asking this as an issue report, but rather, wondering if there's a repopulation or something to add the field back in if it's ever missing?