I bought a pack of 4 yesterday and gave 2 to my boyfriend. I swear they weren't even in his crocs for an hour and he lost one. I am putting them in right so i don't know how it is happening. The only thing I can think of is that they are really 2 pieces and they are snapping apart. I have an off brand jibbitz and when I lost one of those it was in 2 pieces. I snapped them back together and pulled as hard as I could and couldn't get it apart again.
Maybe I should send jibbitz an email.