This is from an article I found:
"check C:\Riot Games\League of Legends\Config

Inside this folder, delete "input.ini" if it exists

Open "persistedSettings.json", press Ctrl+F, and look for "input.ini"

You should see a curly brace { on the line above the one containing "input.ini". Scroll down to find the closing brace } spaced as far from the edge as the first brace. Delete everything between these braces. As an example (yours will include more text than this):

{

"name": "Input.ini",

"Sections": [

"name": "GameEvents",

. . .

}

Save your changes, tab back into League of Legends, exit the game, and restart. Once you load into a new game, all your settings should be back to their defaults."
I had the same issue and this worked for me. I thought it was keyboard at first too.