Old timer at the bindery in Sacramento warned me about PVA on leather, and he was dead right
Back in 2019 I grabbed a bottle of PVA and started pasting down a leather cover on a rebind because it was faster than wheat paste. A guy named Ray who had been binding books for 40 years told me plain, "You'll regret that in a year." I brushed him off. About 14 months later the spine cracked right along the hinge and the leather had gone stiff as a board, no flex at all. Pulled it apart and the PVA had soaked in and locked everything up. Anyone else got a rule they ignored and paid for later?
Worth pointing out that PVA itself is not the whole story here. Straight PVA dries hard and has zero give, so on leather it will fight every time the cover moves with the weather. But a lot of people mix it with a little wheat paste or use a flexible PVA meant for book work, and that holds up way better than the plain stuff from the hardware store. The trouble is that most folks grab whatever is cheap and fast, just like you did. Ray was right for the wrong reason maybe, in that the issue is less "PVA on leather" and more "the wrong glue applied thick.