I'm having two issues with this instance while using a 3rd party app: Sync for Lemmy. Both issues are about blocking communities, and I don't think either are the app's fault.

Failing to record new community blocks

The Sync app fails to record a block when I use its "block community" button. This request either doesn't reach the server, or the server is mishandling it. I get no error in the app, but when I check my block list on the website, the block is not there. This feature works fine on other instances.

Failing to apply community blocks

When viewing the instance in Sync, none of my community blocks work at all! I have 68 blocks, and as far as I can tell, none of them are working. I verified 5 that definitely are not, but its hard to know if I'm not seeing a community because a block is working, or I just haven't scrolled far enough to see any posts in it.

On the other hand, when viewing the website, the blocks do prevent those communities from appearing in my feed. They just don't block them in the feed the Sync app receives from the API. Blocks on other instances work fine when that instance is viewed in Sync.

So it seems like there are two bugs regarding blocks at the API level.