Its just a slow start to the season and he will have a fair amount of impactful games this season which will be very long. I'd rather have mahrez playing badly at the start of the season as compared to the business end where you really need your top players to do well and he has consistently been doing that, some players just don't get the same love as others, it's an undeniable fact.
I also find it absurd and hilarious that people are questioning his contract extension, he was one of the top players last season, further, we lost three integral members of our squad so it was good on part of city and pep to extend his contract. True value of players like Mahrez is felt when they leave, there must be reason that Pep values him so much and sees the things which his critics can't.
By February, march alot of people will be very happy to have a player like mahrez in our squad, just give it time