If everything is fine, your belt was/is to long.

I have seen some aftermarket belts, which are supposed to be exact
replacements, be too long or too short.  And, not all aftermarket belts
may be of equal quality to the OEM. Maybe your belt has stretched?

Last, I had a heck of a problem with belts on a GM Fiero after a
factory recall.  Seems the dealership mechanics cut some corners,
did not reassemble the pulley and tensioning system correctly after
the engine work was completed.   It was a continuous problem with
belt slippage, etc, until I got it up on a rack, assessed the problems
which the mechanics had caused, and refitted and adjusted everything
correctly.