Farcaster

been having some issues casting to certain channels, where the dropdown says "not available" even though I've posted to them before

I haven't been online and casting very much this past month, did I miss some kind of update to channels that would cause this?

Yup. You now need to be a member of a channel to top level cast. You can reply though. Look underneath the channel banner image and there's usually some guidance on how to become a member.