[Gameplay] Elise Spider Transformation Delay

I've noticed a lot now, and had people tell me the same, that Elise's Spider Form doesn't always trigger when you press it, in combat. I don't think I've ever actually had this problem outside of combat, but I know it happens frequently enough for me to remember. It won't be on cooldown (haven't used it for dozens of seconds or even minutes at a time sometimes), I won't be stunned or prevented from casting, but it still refuses to go off after repeated presses -- sometimes mashing -- of the R button, sometimes not at all until running away.

I can't really say there's any way of replicating this effect in a step-by-step basis, since I don't even know what's causing it.

I have noticed that it seems to happen a lot under any kind of crowd control or AoE effect, none in specific, though I can't say for certain that it has any relation to the issue either. I just know that sometimes the forms just refuse to switch for no apparent reason at all, even when everything else works.

This happened to me most recently when fighting Nidalee in our base. I snared her and released my neurotoxin while autoattacking her. She was clearly unable to prevent me from doing so because she was snared. Even still, it refused to let me transform for about two whole seconds, at which point it screwed me over and she killed me because everyone knows that Elise's damage and sustain are really bad in her human form.

I will post more information about this issue as I discover it.