Crack in paint seems to be slowly getting longer
Unfortunately many of the homes built in the 80s and 90s have features such as vaulted ceilings and floating walls, and they usually employed engineered truss systems. Those trusses move seasonally due to temperature and moisture changes, and builders hadn't yet worked out how to handle that movement.
In later years devices like isolation channel and expansion joints were installed, which allowed for such movement without drywall damage. Your house (and mine) lack these preventative measures, so we get cracks that come and go.
You have a couple choices, if this in fact the problem you face.

Ignore it.
Rub some paintable caulk into the cracks, then paint. Press firmly and don't leave caulk on the surface to create ridges or seam lines. A lightly damp cloth can help. Such caulk shrinks as it dries, so you may have to hit it twice.
Re-tape those areas with fiberglass mesh. Obviously this requires re-texturing and full-wall painting. Stronger setting-type joint compound (like EasySand 90) for the initial tape coat would be a good idea. Pre-mixed mud is easier to finish with.

All that said, I'm speculating. If you have reason to think you're in a termite area or have larger foundation issues, bring in an expert to look with real eyes.