When I tell plex to record all episodes (new and repeat) of currently airing shows, it will do it just fine, but when I tell it to record all episodes of a series that is no longer making new episodes (only reruns) then it won't record anything. If I click on the series after I tell it to record all episodes then it will say that there are no upcoming airings.
If I record only a single episode instead of the entire series then that one episode records just fine.
I have also discovered that after I successfully record a single episode, I can then go back and tell it to record all episodes and it will work successfully. It's kind of annoying, but at least there is a work around.
Currently I am running media server beta 18.104.22.16872, but this was happening also with the public 1.10.x. I have the server installed on Ubuntu LTS 16.04. I have the HDHomeRun Extend.