RMMV Bug screen "gradient", "canvas" etc

[Indinera]

A player got the following bug (needless to say I never got it in like 50 playthroughs).



What is it saying? Any clue what's happening and how to fix it?

 

[caethyril]

This means a battler has a non-numeric value for their HP. The default code has a safety check in place to prevent this error (non-numeric values become zero), but I'm guessing you're using Yanfly's Damage Core plugin, which removes that check.

The cause is likely an error in a skill formula: something doing non-numeric (e.g. undefined) damage. It could also be worth checking any scripted damages, i.e. anywhere you've used gainHp.

 

[Indinera]

Oh I see, very interesting, I'll look it up.
EDIT: all your suppositions were correct.