Virtually all modern cabinets are built out of plywood (high end) or particle board (standard grade) with solid wood face frames, if you have a face frame style. Plywood and particle board moves much less than solid lumber due to humidity changes, so it is unlikely that movement of your cabinet is the problem. As to the truss uplift theory, it only applies if you have trusses, and it only affects the ceiling gap, it does not cause the wall to move laterally. Also note that the OP stated that the problem is occurring both on the first and second floor.
I iterate, the most likely problem is movement of the studs due to moisture changes. Drywall dimensional changes due to moisture fluctuations are very small, not likely to be the cause of this issue. As to the note that cabinets are screwed tightly to the wall, so movement of the wall could not open a gap, check out your connection, it is almost certainly not as rigid as you think, and if the stud shrinks around the screw shank, you can still open a gap without violating any laws of physics. You need to consider how a change in dimension of a stud would affect a screw, it is not as simple a geometry problem as it sounds.