This question is about this user on TeX.SE.
He is suspended network-wide for one year, from 23 April 2019 to 23 April 2020, after a conflict on TeX.SE Meta.
As I read in this article, he can't vote, ask, answer and comment.
However, looking at his activities, he can still post questions, answers and comments, like any unsuspended users.
How can it be possible? Is there a hole in the system?
This is only one particular case. I believe there are many other cases across the network.
From this answer by Jeff Atwood, he probably posted as a new user and then had his accounts merged. I think there should be something to fix this bug (this is definitely a bug), by e.g. not allowing account merging on suspended users, or only allowing account merging on any user a limited number of times. Otherwise, the suspend system clearly no longer works, and that is not something we want.