tl;dr: I suspect all you need to do is manually download the newest version of Plex from Plex.tv and manually install it through the MyCloud web interface. Remember that you need to download the specific compile for your specific Western Digital device.
I finally decided to tackle this problem on my Western Digital PR4100 MyCloud. Here are the steps I took to repair it. I don’t know which step fixed it so some may be optional.
- I logged in to the drive’s web interface in a web browser (Chrome, http://192.168.0.33)
- I clicked the Apps tab
- I selected Plex from the install apps
- I flipped the “Run App” slider from On to Off
- I waited a few seconds and then flipped it back on and immediately clicked Configure when it became clickable (which brought me to http://192.168.0.33:32400/web/index.html)
- Very very slowly, it brought me through the Plex login process
- Very very slowly. Be patient.
- I fiddled around in settings, trying to turn on Remove Management, but was unable to make the server remote-accessible.
- I downloaded the newest version of Plex from the Plex website. Remember: Plex for WD doesn’t automatically update. You must always manually install updates. (Go to the link, click Western Digital from the drop down, then click Choose Package to pick your specific MyCloud device. https://www.plex.tv/media-server-downloads/#plex-media-server)
- I went back to the Western Digital MyCloud web interface and clicked the Apps tab again.
- I followed the normal process for updating the app:
11a. Select Plex Media Server from your Installed Apps.
11b. Set “Run App” to Off
11c. Click “Install an app manually”
11d. Click OK to re-install the App. - I may have power-cycled the MyCloud drive. I don’t remember.
And ta-da! After doing the update I was able to click Configure for the Plex Media Server again. The process didn’t lose any of my media or settings.
(http://192.168.0.33:32400/web/index.html)