Strange they have both lost them, do they get out / anything new they could have gotten snagged on ?
They're indoor cats, so the collars must be around here somewhere. I'm suspicious because when Riley was a kitten he learned to scratch and twirl the collar so that the catch was under his chin, then get his mouth round it and bite down to release it.
He would then run off with it and stash it under the bed
He hasn't done this in over a year, but frankly I wouldn't out it past him
I suspect they've just been playing rough and they've come off - Riley tends to "tackle" Skye by grabbing her by her scruff, so he might have bitten down on the catch and released her collar (she's never learned to get it off herself, unlike him).
The really baffling thing is I can't find them! Mind you, they are prone to playing with things like collars, and running about with them, so they may have been co-opted as toys and been dumped in a corner somewhere or under the bed
Max managed to get out of his new collar a few times as well the other week, not sure how! He has a Kitty Collars one and the clasp etc is absolutely fine.
Maybe they're just telling us they don't like the colours 
you may have a point! They both just have plain blue ones, so perhaps I should get some collars more suited to their tastes!
