I'm also having this issue and it seems like it's happening to us because we have custom ability keybinds set. It's happening to me a couple times a game and leaving/rejoining fixes it.
Awful quality recording, but here's mine doing the same key animation but no cast for heal I have bound to Q
It happened again later in the same game to quantum entanglement on E, so it's not about which ability or the key. The only thing in common I noticed between them was that both times I died with that ability on cooldown, and then couldn't use it after respawning.
Oh, also the first time this happened for me was last Friday (8/22) and I played a couple games Monday (8/18) with no issues.