EVERY TIME

This could be happening for a few reasons, so I'd like to help! Firstly, make sure that you have League installed on your primary, internal drive (usually C:\Riot Games\League of Legends). If you have it on something like a thumb drive then your files would only be saving temporarily, causing the patcher to apply new game files every single time you launch it.

On the other hand, you might have really tight security settings through your OS or some anti-virus that's preventing your game files from being scanned or repaired. You'll want to go through each step of the permissions guide to make sure League is being added as an exception. Hopefully that will get things fixed up!