Not always, but sometimes, if I’ve edited a mesh (even a simple plane), I can no longer subdivide, nor add loop cuts. Is this a bug, or is there a reason for this. I would upload a blend file but the issue is not consistent. Sometimes, if I delete the original mesh and start over, everything is OK. Confusing for sure.
Check the faces are actually quads (no subdivided edges, duplicate vertices etc). Triangles and faces >4 sides cannot have loop cuts
Well, then wait till this happens next time, save the file and provide that… Unfortunately your error description is a bit generic - not sure what we are supposed to read from that alone.
Are you sure you’re not generating n-gons with your mesh edits? Because Blender can not detect loops across n-gons and subdividing a n-gon will only produce another n-gon = might not have an immediately visible effect.