Preframed doors seem to give lots of people a problem.
I once bought a brand new house from a contractor with good reputation. I'm sure it wasn't a matter of a "rush job" as the house had been advertised for sale for several months.
About 6 months after we moved in, I noticed that a "gap" had developed between the door frame and the adjacent floor tile. On investigation I found that they had placed the pre-hung door quite neatly into the hole framed for it, but had failed to install even a single nail or other fastener to hold it in place.
Burgler-proof steel door. Massive key-locked dead bolt. Not fastened to a single part of the house.