I'm using containers in proxmox, and doing that fix seems to prevent the container from booting after a shutdown. I didn't get any of these issues a couple of months ago doing the exact same thing.
I'll save you a click, this is the answer I mentioned above:
That being said, what guide did you follow or how exactly did you set up plex?
When using systemD services like plex its important to distinguish, running it yourself under your user account, and running it as a system service with a non-privileged no-login account.
I used the container Ubuntu 16.04 and still got the error, seems that it has no issue with systemd.
The guide shows that it should work out of the box on ubuntu 16.04
My error is like the one on the original post. The question is why is there an error on the first place? I had no error with an older version of plex a couple of months ago doing the same steps.