I'm not even surprised when I see Cait lose to Vayne anymore
First couple times I saw the classic counterpick lose this season, I assumed it was just the inherent insanity of the new ranked season. But after the first couple times, I still haven't seen a Cait actually do well against Vayne; at best she won't instantly feed outright.
There's actually an obvious reason for this: for Cait to beat Vayne, she actually has to poke. This is Cait we're talking about, but most adcs in low elo don't even try to poke and I don't expect it of them (I'm happy if I get one that doesn't try to solo towerdive level 3, currently). Cait beats Vayne in a high skill matchup, but a lot of low elo Cait players just use her because she's safe and strong in lane; they lack the mechanical skill to do more than farm with her and don't understand that Cait is basically an anticarry in that if you pick her you need to win lane or you'll get shafted later.
Vayne players, on the other hand, come in two flavors: the stereotypical ten yearold whiny Vayne that tries to melee people to death 1v5, or the Vayne that's actually competent at both the role and the champ. If you get the latter in lane against a bad Cait, she wins every time.
Hope I made one aspect of low elo less confusing for everyone who got shafted in provisionals.