Healing spells landing on me instead of my target

[Viviza]

Just a guess, but you may have been a little too aggressive with target swapping and casting at the same time. You started your heal a split-second before the swap, when normally you do it a split-second after. From your point of view you did it 'the same as always' and it feels very jarring to see your cast 'miss', but in fact you mistimed things.

It's an easy mistake to make when you're used to swap-and-cast by muscle memory. I'll do it more often when I'm tired.