Others are not broken, such as !twoxchromosomes@slrpnk.net.
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It's not a general functionality problem with subscribing or blocking. If you go to any thread in a community, the buttons work from there. It also works to sub from the community list.
Hopefully this will be fixed in the 0.18.1 Lemmy release that is almost ready.
I've found the same thing, if you change the sorting (Hot/Top/New/Old), switch between Posts/Comments or switch pages (even if the second page is empty), the buttons start working again too.
Alternatively, you can click the 'create a post' button and go back to the previous page; this works well for me.
Here we can discuss anything about this Lemmy instance/server itself.
Our XMPP support chat: Movim or XMPP client.