So I opted for option 1. I did go ahead an update my "production" Emby install to 5781.4 which went smoothly but of course did nothing to fix the problem.
I then downloaded the PBI you linked to and uploaded it as a new jail in Emby as can be seen here:
Next I assigned it the same storage as my production plugin and fired it up and imported just my DVD media folder and let is scan it. But then, when I started poking around, this is when things got wonky.
Here's a screenshot of when I went into Movies for the first time:
Notice the missing thumbs and the one that is interlaced or something?
Next I clicked on the Movies tab, and all I got was the following empty screen:
I then clicked the little gear icon in the upper right to get back to the dashboard. But here I just had the spinning wheel:
The only way I was able to recover was by closing that particular browser tab and go back to the same url again.
When I did, I got the following, this time with a different "interlaced" image and a bunch of empty ones:
I then shut down the plugin and restarted it. When I went back in, I got a little further on the Movies tab as it now at least gave me a count of how many movies were in my DVD folder, but no thumbs.
So something definitely appears to be "off".
Again, my production Emby instance is running just fine (except for the slowness when running the CoverArt Plugin).