This is still happening, I know for a fact. Just now I was in a game in which I was unable to change my summoner spell. I closed and relaunched client, logged in, still in queue, was unable to change spell.
tl;dr Unable to change summoner spell, logged out and back in 3 times while in champion select, never interrupted. Left before the timer hit 0, sucessfully dodged. Still salty I had to dodge a ranked game because I couldn't change smite off Xerath mid. Not sure how much LP I will loose in total as a result due to tilt over this incident in further games.
https://boards.na.leagueoflegends.com/en/c/bug-report/txTOmQrx-unable-to-change-summoner-spells-spell-select-box-appears-completely-black