Given the scenario you are giving...................
I'd be looking at how the shelves in question were stored BEFORE you received them. Were they all in one shipment? Were they all tat the distributor before you go them or shipped direct from the manufacturer?
To me this sounds like either an original manufacturing defect, or a defect caused by the way the shelves were handled in storage or shipping.
How do you STORE the shelves in your studio?
Failures happening in too large a range of conditions.
I have no idea how they were stored before they got to me. From what I can tell, the distributors don't stock Corelites, they order them and have them delivered to them or drop shipped to us. I can't speak to how they may have been stored before I received them. We store them on their edge up against the wall in the kiln room. That was up and until recently, I added a set of padded hooks on the walls in the kiln room, now they are stored on the hooks / on their edge up against the wall to keep them off the floor.