I am having issues subscribing to !piracy@lemmy.dbzer0.com, but I do think it also happens with other communities on different instances.
I subscribe via the main button or via the plus in the search function. The community may appear in the sidebar, sometimes it does not at all, but whenever I restart the app the subscription is fully gone.
Weird thing is, on another app for lemmy I can still see I am subscribed, so I am not sure what is going on.
Hm, I have an alt account which I synchronized with the Lemmy handshake app. That one is subscribed to the piracy community also in Eternity. I switched off the account sync via handshake a while ago, so this is not an artifact of that.
Also, I just checked the “subbed” tab, there I can see posts from the piracy community, which again suggests to me it is just some bug in the Eternity app not showing it as subscribed when going there or in the subscription list.