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No idea, I mostly use reddit to lurk around the subreddits Gridcoin and Pokémon Go (sshhh ;-)).
I haven't posted anything abusive to get a shadowban, few weeks ago I posted a support post that is still visible, my next post was me questioning why there's so much hatred towards Erkan.

There is a sub specifically to check if you are shadowbanned. You post in it, and people reply if they see your post. May be worth a quick shot.