you can get shadow banned from subs for posting on other subs and its all automatic as well. this I know first hand as I was a regular poster on an antique related sub only to one day find none of my posts getting noticed and the pictures not showing. came to find out they are part of a group of subs which ban people who post on another sub.

reddit has become a real cess pool and its not the users and what they post but the back door rules and such and pettiness among to moderators of many subs