I had a crack develop on an interior wall at the upper corner of a doorway. I cut out a piece of drywall about 3 feet wide and 2 feet high and replaced it. The piece is 'L' shaped so that there isn't a joint extending up or horizontally from the corner of the doorway. I was careful to make a clean corner on the inside corner of the drywall before installing the replacement piece. After several months, another crack appeared at the corner of the doorway in my replacement piece. The joints at the top and bottom of the patch are opening up as well. I used paper tape and premixed mud. Both sides of the wall have the same kind of crack. The house is around 15 years old. The crack seems to open and close over extended periods of time (months). Not sure if it's seasonal or what.
What can I do to prevent this from happening again (after I repair the corner again)?
One thought I had was to glue and screw some 2x2's on the studs so that I can glue and screw plywood flush with the existing studs. Then cover with drywall as usual.