Years ago, the tennis bracelets I repaired all had the same exact problem, rivet failure.
All were of Chinese origin, but failure occurred even on repaired rivets. Therefore, I assumed it was because the 14kt rivets were very thin. None were thicker than 38 gage. I couldn’t change the thickness of the rivet, but I could change the metal.
With repair-weary owners’ permission, I substituted red brass for the gold rivets, and those brass rivets never failed. I know they didn’t fail because over time, I eventually replaced nearly all the rivets in a few of those bracelets.
Those bracelet owners did not care about the brass substitution because they said it saved them a thousand dollars in never-ending rivet repairs.