I did read OP 5 times just to be sure i get you right
Cause i have strong doubts on what is causing it
I want you to test few things
Cause all you have in events is perfectly fine in my eyes
DO NOT CHECK these things at a same time
One thing at a time
Here at beginning of scene
Set hp max to exactly 240
And now check if when you pick up heart you still get -30 or will it be 10
Next here
1st thing to check
Add 50 and check does it will end up with - 30 or -50
2nd under change hp max add 30 but above delete health so between them
Add change HP add same value as you add to HP max
Tell me what did you get