There were three checks apparently. One to see if he was offside which he wasn't - a good foot onside. Second to see if it was handball which it wasn't and third to see if it was a penalty which it was bit VAR decided it wasn't. And then for some unknown reason play restarted with a free kick for Everton from where Mahrez was perceived to have been offside. All of this took more time than was added on at the end of the half despite the VAR check for the goal as well which took a minute or soFor the Mahrez one there were two checks.
1st to see if he was onside or off. It proved he was onside.
So then it was looked at to see if the resulting challenge in the box was a penalty or not. It wasn't given.
I assume the ball went out of play after the challenge - so Everton were awarded a goal kick????