There are two horribly synergistic bugs on my favorite NSFW instance, lemmynsfw(dot)com:
Sync's community filters don't work on that instance, and that instance's community blocks don't work either! They're not related, I'm sure, but when both are broken I see things I can't unsee.
I built up a huge list of community filters in the app, and then one day realized not a single one was working. Not even if I cleared the whole list and added just one filter. Refreshing didn't help. Nor did clearing the cache. At least, I think I tried that.
And, for some reason, Blocks don't work on that instance either, but only when requesting my feed through the API. Blocks do work on the website itself. But that's not your issue. That's theirs.