Some clears, like PPG Concept, will shrink for a very long time. If an area was still swollen with a lot of trapped solvents, you may have sanded it flat on a high spot, only to have it sink in as the solvents slowly escaped.
An example would be when I allowed the paint on a Shelby Mustang to dry about 4-5 days... sanded out a couple runs in the Concept clear, then buffed a couple days later. Looked good! Two weeks later, the spots that had runs sank in creating "dips" in the shape of a run. Undoubtably the most unstable catalyzed clear I have ever used!
I called a guy on a chat group who only uses the Concept line, and he advised me to wait six months, then sand and buff again..............
SAY WHAT!!! I need products that work every time, and also allow the jobs to be completed within a reasonable time. I will never leave my DC92 Diamont again! :-)