I upgraded my server to version 1.15.4.994-107756f7e a few weeks ago. Since then, the plex app on my Roku reports an error. It says my server version is 1.7.xxx, and must be at least 1.10.xxx.
The Plex apps on my Apple TV and my Amazon Fire stick and Amazon Fire Stick work just fine.
I logged onto the Web App to download the log file, when I noticed a new version of the server was available v. 1.15.4.994, So I just went ahead and installed that. Now it all seems to be working.
That’s the version you said you were already on. Maybe you only downloaded the update and never actually applied it. Oh well. As long as it’s working now.