I've used tapas for quite some time but i don't think shadowbanning has ever been a thing on the site 
At most I've known of series not appearing on mobile but still showing up on desktop for content moderation reasons but not more than that unless a series was flagged for something or taken down
If anything I'd imagine the best course of action would be to try to reach out to Tapas staff via email or with a ticket on the official discord server if you havent filed one already. otherwise you'll just have to be patient in waiting for a response since they probably get a lot