For maybe three of those eight I can say it *may* have been due to a slight bump. I can attest that although I try my best to be ultra careful with y equipment, accidents do happen.
But in most cases it was simple normal wear.
In several of the cases, it was within a few days or even a few hours of use since the previous repair. (sadly, often after sitting on a shelf for most of 90 days and thus out of warranty of the repair)
So no, not necessarily rough on the lenses. They are just crap.
I now rotate using my backup lenses often to make sure they get well used within that warranty period since I cannot trust that the repair will last more than a few hours.