Plex removed artist from my music library after I added "Poster Art"

You should use “Plex Music” for both Scanner and Agent.
These are the defaults when creating a new music library.

Okay, I changed it. Nothing happened.

I see now that there is an option to checkbox “Prefer Local Metadata” now. That was not an option under the “Personal Media Artist”

Yes. But you should only enable it, if both your folder structure and the embedded meta tags follow the guidelines I laid out above.

You should also take a look at the rest of the articles here https://support.plex.tv/articles/categories/your-media/naming-and-organizing-music-media/
in order to learn how to add your custom artist photos and album art jpg files.

What happens if the folder structure is wrong? I know they are all correct, but I want to make sure that I can enable it, without messing things up.

Embedded meta data from one release can override those from other files – i.e. chaos.
You don’t want to deal with this.

Oof, I definitely won’t enable it then.

So, after going through all the steps and checking the Metadata, I still can’t get those two artists into the library.

I’d start by inspecting the currently embedded meta data very closely.

Here is how it should be looking.
You can see both the folder strcuture, file names and embedded metadata in this screenshot.
As you can see, I have only two tracks from this album. But that doesn’t matter, because I have “prefer local metatags” enabled, and I am following all the rules from above.

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So, this looks to be correct. I only used one album as the example.

This looks alright, but avoid a disc number being zero.

So the path that you added to your plex music library should be exactly
E:\Andy\Music\PLEX Flac Music\
Not even one folder level above, nor below of that.

Ah, ok I will change the disc number.

The path is correct then. That’s exactly how I have Plex set up.

I have gone through every albums metadata, and I have not seen any issues. I cannot get Plex to add the artist back into the library.

The Plex Dance
With music, you can omit step 4.

I have also done that. Lol. One of thew first things I tried before coming to the forum.

Huh, it actually worked that time. Weird. Plex Dance FTW. Thanks for all the help! I really appreciate it.