I used regular paper tape,
and it seems that is where it is occuring.

Is the mud, only, cracking or can you tell if the tape, itself, is
rising (peeling up, separating) from the drywall surface?

If you can be sure only the mud is cracking, then you are caking the
mud too thick and, as it dries, it will form irregular cracks, usually
in all directions, like in a dried-up mud hole cracking irregularly
from drought. This isn't bad. Allow it to dry completely, gouge out
or scrape (not sand), somewhat, those areas and skim it again.

If your tape adherence, to the drywall surface, has failed, this means
you didn't put enough mud behind the tape for it to adhere properly OR
You may have initially put enough mud behind the tape, but you pressed
the mud out from under the tape (when skimming, too tight, that first
mudding/taping layer). The cracking, due to this lack of mud behind
the tape, will likely be a straight lined crack along the edge of the
tape (and not the small irregular type cracks as that of a dried-up mud
hole). If this is the case, cut out the mud and tape, from the
affected areas, and re-mud and tape. If this is the case, you may have
mudded and taped improperly, this way, over other areas and your
problem may very well show up in those other areas, later.

I hope your problem is the thick mud problem and not the non-adhesion
problem.

Sonny