YES I HAVE IT ITS SO ANNOYING
I sent a ticket a week ago, the support team couldn't fix the problem, so I sent a bug report too, they didn't fix it yet... It's so annoying
https://boards.na.leagueoflegends.com/en/c/bug-report/mOpGTnHF-client-using-mb5-and-mb4-alt-tabs-me-out-of-the-game provides potential workaround