And it's nothing new either. Xhaka, Mustafi and Pepe have been racially abused for years online, and many times even worse if you see some of the comments on Mustafi's social media.
Generally speaking at the top 4-6 clubs certain fans start coming out of the woodwork with their racist shit when they need a scapegoat for bad results but there are other clubs who are much worse who feel more like those Italian clubs. You saw some of those protests with the taking the knee that happened at some clubs, as well as the shit that Chelsea fans come up with outside the context of any game. It's disgusting.
We are nowhere near as bad as the worst but just like most other clubs, we have some fans who come up with some vile shit safe in the knowledge that they are anonymous. I hope they identify those 16 supposed season ticket holders who were racially abusing players on twitter and ban them from ever attending a game again.