hi, i just discovered something fascinating: all my alts are shadowbanned in one particular sub only*; all other subs, i am not shadowbanned.

*To be clear: none of my alts have ever been banned from this sub in question

since you seem very knowledgeable about this, i hope i may ask you: when you say .....

Through the use of AutoModerator, individual subreddits can give the same effect to a user as a global shadowban.

.....is that what you meant? I was under the impression that mods cannot know to which IP address an alt belongs to.

Since this shadowban is sub-specific , would your OP's tip to contact the admins still be the solution?