Was Jerboa the one crashing on opening?
I was also having the Jerboa startup crashes. Version 0.0.35 fixed it for me (it might not be on vanilla F-Droid yet but it is on the IzzyOnDroid repo)
Are you actually looking at it from your instance? The post should say via myinstance.com at the top. I think there is someone working on making this behavior more intuitive. Also I posted this on liftoff.
I've got the same problem. In order to subscribe to communities from different instances I need to do it through a browser first. Only then I'm able to post using liftoff.