Tahm Kench Bugged W with Enemy Rakan Ult (Charm)

Hi, I recently just played a game with myself as Tahm Kench support and the enemy support being Rakan.

After my ADC (Varus) was hit by a Rakan Ult Charm (around level 6 in lane) I pressed W close to the same time and devoured him to save him.

After once instance like that I was unable to devour Varus for the rest of the game.

Anyone else have bugs similar to this potential charm bug with Tahm Kench's W?

In case it matters here is the list of all champions in that game in case potentially there was another factor involved.

Blue Side: Top - Rengar Jungle - Kayn Mid - Vlad ADC - Varus Support - Tahm Kench

Red Side: Top - Ornn Jungle - Jax Mid - Zoe ADC - Xayah Support - Rakan

I hope this information can give some insight to this potential game breaking bug.

Thanks.

EDIT: This is of course on the current patch 8.2.