What is a door issue?
Door issues come in a variety of forms, but the one thing they have in common is that the door does not fit squarely into the door frame. My procedure to judge whether a door issue is related to slab foundation distortion or not requires some knowledge of how interior and exterior doors are installed.
The front door
To reliably assess whether a front door has issues that are caused by foundation distortion, there are some facts that should be kept in mind.
The front door is in a class by itself. It is normally the heaviest door in the house. It is exposed to the weather on the outside and conditioned, drier air on the inside. To accommodate weather-stripping, this door is installed to a more precise fit than any interior door.
Even though the front door is normally the heaviest door, it is usually supported by #8, 1/2 inch long wood screws. These screws should be replaced. They are too weak to prevent a thug from kicking the door in, much less properly support the door over time.
The solution is to replace the 1/2 inch screws with #8 screws with 2-1/2 inch long. The longer screws will go through the door jamb and penetrate the door frame.
I always open and close the door. Make sure the door the door fits properly. Check to see that the door latches in a normal manner. Hold the door open and take the door by the doorknob with one hand and with the other grab the top corner. If you can move the door, there is a good chance that any irregularities are due to the door, not to foundation distortion.
Another thing to do is to observe the floor covering noting if it is floor tile. If it is, check to see if there are any cracks that run from one tile to another. If so, that is strong evidence of foundation distortion.
Other exterior doors
The only difference between the front door and the other outside doors is the weight.
Interior downstairs doors
If a downstairs interior door frame is distorted, it is likely to be due to slab foundation distortion unless there is evidence that suggests otherwise. Check to see if the door is loose like I recommended for exterior doors.
Interior upper story doors
I cannot see how slab foundation distortion can affect an upstairs door. The obvious that the culprit is either the door itself or the wood frame sagging.
If the house is over 10 years old, then creep distortion is a significant factor. The problem can also be caused by the way the door frame was constructed. It is not unusual for a door frame to be supported by a joist directly under one side of the door frame while the other side is supported by the subflooring. The subflooring will sag under the door frame causing the door frame to rack.