[8.21/8.20] Having Hexflash can lead to not being able to use flash all game

Twice within the last few weeks, once on EUW and once on NA and on both 8.20 and 8.21, at some point in the game my flash just stopped working. Both times I had Hexflash equipped so I would assume it's connected to that. The button is grayed out and says "you can't use this right now" when pressing it, but pinging it shows that it's up. Reconnecting didn't do anything.

Here is the most recent game in question, the other one was on EUW also on Leona: https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2894702641/227680785?tab=overview

I don't know how to replicate the bug since I didn't notice it instantly, a teammate said it can happen when you die while casting Hexflash but that didn't happen either time.