Haii! How are you? I'm fine!
So, i saw that a lot of PBE players are getting this (i got this twice btw :P) and they don't know how to fix it, bug i know a way! (Maybe there is another way, but i use this method.)
To fix it, you have to re-install PBE (yes, RE-INSTALL). I don't know why you have to, but... it works, lol.
If you don't have the PBE installer, here is the link: https://pbesignup.na.leagueoflegends.com/en_US/pbe
I hope i helped you fix this bug! If you know another way, let it on the comments!
Have a great day!