It sounds like you are not believing that there’s a problem at all.
It is obvious that in any large real-life library, people don’t take notes when changing posters and HOW they changed posters (taking another existing one or uploading a new one).
This way, you will probably never get a detailed “proof”.
Here’s how you can still test this without leaning back blaming users of not providing enough evidence:
a) take one small sample movie in a folder. Create one black with a white dot in centre named poster.jpg (make sure it’s something easily identifiable).
b) Create two lists of - let’s say IMDB’s Top 250 movies (using the correct Plex naming) in a text file - one in English one in another language Plex supports (German, for example).
c) create a five-line script to copy that file/folder 250-times and rename both copied file and folder using the English list. Move those 250 movies into “library base folder 1”.
d) do c) with the German list, moving the 250 movies into “library base folder 2”.
e) change both scripts to add the same poster.jpg to all newly copied/renamed folders. and execute both scripts again, this time using “library base folder 3” and “library base folder 4”.
f) Copy “library base folder 1” and “… 2” to "library base folders 5 and 6…
Now you should hav 1500 movies in six base folders (6 times 250), half of them with English names, half of them with “Language X” titles - one third of them using a local cover art asset, two thirds of them not.
f) Create a new PMS with standard settings,
g) create six new movie libraries using standard settings, three of them using English language, three of them using that foreign language you chose. Make sure that you prefer local assets and add one of the four library base folders to each of the four libraries.
h) Make sure that Plex gets the identification right in all six libraries and check if all local cover art assets are being correctly used.
Now, in the first two libraries that do not have local cover art already applied, add the same Cover file via each movie’s Edit Metadata UI.
At the end of this process, all movies should have the same image as Cover art in four libraries - applied differently.
Now go to libraries number five and six - again make sure that all movies are correctly identified by Plex… and change the poster for all 500 movies to something which already exists - let’s say the third available image. Take comparision screen shots for all two libraries.
Now, save the LOGS…
Every morning, quickly check the first four libraries for changed posters and take logs.
Every week, check library five and six for changes using the comparison screenshots.
Identify the problem of the next couple of months…
You could check for
- larger numbers of test movies
- different library languages
- different applications and sources of posters
Want to make it more complex (to find patterns)? Then do not use the same cover, but covers having only numbers and perhaps different file formats.
Too much effort for you?
Anybody else volunteering?
Somebody else from Plex staff? Users should only be asked to take a more “USER” approach of helping you finding the problem.
But of course, this can only be done if somebody would really be interested to find the real cause.