I suspect that most first batch Series 0 watch in 2015 has this problem. My Series 0 watch was repaired (replaced) for 2 times before they gave me one that won't pop off every few months. The repair was free even after the warranty period. So I think for Apple devices AppleCare isn't really needed since if it's Apple's problem and it's widespread they nevertheless replace yours for free. Mine didn't get upgraded to the Series 1 since it was a Stainless Steel version.
Afterwards I just gave up on the Stainless Steel model and use the saved cost to upgrade to a new generation.
Afterwards I just gave up on the Stainless Steel model and use the saved cost to upgrade to a new generation.