I think the person saying that if Toby puts in that performance he doesn't get criticised as much is absolutely correct BUT Sanchez has been doing it time and time again and IMO has regressed a lot this season. I've picked out a few instances from the game where his positioning and decision making was really poor to show this.
GOAL
This is the goal, not entirely his fault but if Toby is in this position he would shuffle across to the area highlighted to close off the run earlier and allow one of Winks/Hojbjerg to drop in. Alternatively Dier could come across then Son drops in for the spare man on the far side. Failing to do this allows him to be in the situation to get beaten in a 1v1.
OTHER EXAMPLE 1
In this passage of play he shows one of his worst habits, pushing up in sitatutions where he doesn't need to and allowing space in behind. Here he can either properly push up on Loftus-Cheek and win the ball, or stay put alongside Dier and let one of the midfielders handle it. He does neither, and gets caught in no mans land.
That lapse in judgement allows this situation to develop, where Cavaleiro has acres of space to make a run into once Lookman gets the ball.
Luckily for him here the ball wasn't quite up to scratch and he was able to use his pace to shut him off, but you can see with a better pass how this situation would have forced a goal.
OTHER EXAMPLE 2
This is from a goal kick, again here he pushes up and loses out. For a player of his height and physicality, he really is horrendous in the air and ideally we should have Dier going up for this or one of the midfielders (at least then if Sissoko for example loses the aerial duel we aren't exposed at the back).
On his way back into position here he is sidetracked by another little duel, again he should probably sit off and let one of the midfielders close him down but instead he goes into a duel he is never going to win and leaves Dier to come across - this leaves a huge gap between Dier and Reguilon so that Reid could have easily have pushed up and been in on goal.
Luckily for this one Cavaleiro strayed offside but look how diabolical Sanchez's positioning is here as a result of his previous error. He leaves Dier out to dry and allows the runner in behind. Along with that he just ball watches and lets Lookman over his shoulder too.