I have a Creusen linisher, ie not cheap and very well made. I had a large stock of brand name belts purchased when i moved out here to TH in 2003. 10-12 years later all of them had the same problem you describe.
No matter what i tried, stapling, superglue, hot glue under a press, nothing worked.
So i have a lot of stock of thick backed al/ox strips for hand held use.
Purchased a new batch last year, and hey presto, perfect belts, perfect linishing.
Buy new.