If this is a fairly modern hollow-core door, I would replace it. I had a similar problem with a brand new hollow core door that I got for a pocket door installation.
Many years ago, hollow-core doors had substantial wood around the perimeter and across where the lockset gets installed. The paper honeycomb was glued to the plywood door skins.
The hollow-core door that I bought had a birch veneer, which I thought was perfect for painting. I painted it lying flat on sawhorses with Behr Marquis semi-gloss paint. Once I painted it, the door warped. It was worthless in the pocket track.
I cut it up to dispose of it. When I did so, I discovered that the honeycomb was not glued to the skins, that the skins were made of cardboard with a thin veneer of birch, and the perimeter support was about 1" wide, so you are limited to saw down the door by about 1/2" per side.
Also, they had only small blocks on either side for mounting the lockset.
Apparently the moisture from the paint was sufficient to cause the warp. Perhaps if I painted while on hinges, and if I coated both sides of the door the same day, the door would not have warped.
The solid core door cost $110.00. Plus the cost of the hollow-core door that I threw out (and all the paint that went with it). So the door ended up costing me $140.00 total.
If it warped like that, it is probably one of the crappy new generation hollow core doors. I would seek out a solid core door. Not only more substantial, but more attractive too. (And heavier to carry around--a helper would have been nice.)