If the strength had slowly decreased, a concern I’d have is if the encasement was compromised, though if it broke, I’d imagine you’d be feeling it. If it went from working to not in a short amount of time (like a week) I’d look for biological factors such as increased water retention.
I have one on the back of my hand (gen 1) and it’s never been able to do much other than hold a small screw or two. Can’t really hang anything from it but will stick to other magnets quite well.