Well, believe it because it's true. Look - you're slamming 2GHz signals down that wire. It's not brain surgery, but this IS rocket science, ya know.
Flat cable is flatly

prohibited by E* install rules, but often works.
In your case it sounds like you've got it routed through the moving door part so that it's constantly being whacked. No good. Loosen the fixed part of the door and route it that way - it'll last a LOT longer, especially if you can make some minor modifications to the door frame to minimize the bending.