They popped off when using my old ali rig on the side of the car once.
The woods are also a much softer rubber so one chipped the outer ring seal and lost the ability to stick to anything.
Most likely a small manufacturer defect that you didn't notice until you used them a while. Woods would have replaced this for you for free. For a while I thought that these nicks were caused by people putting the cup protector on in a rush, but there is simply no way to cause this issue with the protector, and if not with the protector, then with what? Manufacturer flaw.
I've also then had the top screw mounts come loose on a few of them.
Only person ever lol.
I do now bring two spare suction cups with me on each shoot just to be safe