Ok - even though I've still got this Internal Server Error, I continued ...
I told "Alexa tell Plex to change my server" - (I only have one server), so it set that one - ok
In Plex, on one of my AFTV's I changed it's name to "Bedroom"
But the Plex name change didn't get picked-up until I restarted my AFTV
I told Alexa to ask Plex what I could Continue watching and it responded with:
Videos on your Continue Watching list:
The last two of these aren't TV or Movies, they're "Other Videos"
I can see "Other Videos" being a problem here, because by definition they will have an unpredictable and probably long filename, and when Alexa reads-out a list of such names, they will be difficult to remember, and probably instantly forgotten.
Next, I asked it to recommend a tv show, and it suggested
S05E01 Season 5 Episode 1 - not very informative ?
I went ahead and played it, and it turned out to be Game of Thrones -
The actual filename is "Game of Thrones S05E01 The Wars to Come.mkv" but this was not shown on-screen
It's also an interesting choice, as I have all 6 GoT Seasons (though I've never watched any of them) - so why select S05E01 ?