This just means that the belt is glazed.
Since you had different stages of different issues with your belt drive system it is hard to nail down.
1. If you have a laser level, inspect the pulley alignments.
(If they are off you should be seeing one side of your belt chaffing.)
If the alignment is off, need to figure out what dies not align correctly.
2. Remove the belt, clean (use soapy water and a medium bristle brush) all the belt drive surfaces. Flush with water and blow dry when done.
3. Replace the belt.
You could probably clean the belt, but I would imagine your time is worth more than that belt.