[frankvw]

I've been battling with this on and off for the better part of two months now and I can't for the life of me figure out what I'm doing wrong. I'll try to include all relevant info in this post, hopefully without including too much, as best as I can. Maybe someone can see what I'm missing (which will probably be something painfully obvious...)

The environment:
Kodi Nexus 20.3.0, included in LibreElec 11.0.6, on a Raspberry Pi 4. All add-ons are up to date.

Under Settings -> Media -> Music the relevant settings (AFAICS) are:
 

• Fetch additional information during updates = ON
  
• Artist information folder = [empty / not set]
  
• Default provider for album information = Generic Album Scraper
  
• Default provider for artist information = Generic Artist Scraper
  
• Prefer online information = OFF
  

What I've done:
I've organized MP3 files in folders by album. I've used Musicbrainz Picard 2.5.6 running on Linux 18.04 (yes, I know that version is EOL, but that's not relevant here) according to the instructions in the Wiki. To illustrate I will include examples of four albums here:
 

• Anjunabeats, Volume 1 (see MB release details)
  
• Armind: The Collected 12" Mixes, Volume 1 (see MB release details)
  
• A State of Trance 2022 (see MB release details)
  
• Hi-NRG Classix (see MB release details)
  

When I display the ID3 data using id3v2 everything looks fine. To illustrate, here's the output for the first track on the Anjunabeats album:
 

id3v2 tag info for 01 Madonna - What It Feels Like for a Girl (Above & Beyond 12_ club mix).mp3:
TIT2 (Title/songname/content description): What It Feels Like for a Girl (Above & Beyond 12" club mix)
TPE1 (Lead performer(s)/Soloist(s)): Madonna
TRCK (Track number/Position in set): 1/13
TALB (Album/Movie/Show title): Anjunabeats, Volume 1
TPOS (Part of a set): 1/1
TCON (Content type): Trance (31)
TDAT (Date): 1310
TORY (Original release year): 2003
TYER (Year): 2003
TSOP ():  frame
TPUB (Publisher): Anjunabeats
TSRC (ISRC (international standard recording code)): GBEWA0310001
TXXX (User defined text information): (SCRIPT): Latn
TMED (Media type): Digital Media
TPE2 (Band/orchestra/accompaniment): Above & Beyond
TSO2 ():  frame
TXXX (User defined text information): (ARTISTS): Madonna
TXXX (User defined text information): (originalyear): 2003
WXXX (User defined URL link): (): https://www.facebook.com/inspirontrance
TXXX (User defined text information): (BARCODE): 5039060169995
UFID (Unique file identifier): http://musicbrainz.org, 36 bytes
TXXX (User defined text information): (MusicBrainz Album Type): album / compilation / dj-mix
TXXX (User defined text information): (MusicBrainz Album Id): 9c36efa5-63a3-4ceb-b886-8151c401826f
TXXX (User defined text information): (MusicBrainz Artist Id): 79239441-bfd5-4981-a70c-55c3f15c1287
TXXX (User defined text information): (MusicBrainz Album Artist Id): 370bd5a3-4abf-4356-8576-3a8fc0c11d65
TXXX (User defined text information): (MusicBrainz Release Group Id): 37a7c7f5-6083-3863-b009-04ee10a67ce6
TXXX (User defined text information): (MusicBrainz Release Track Id): bb41c9ef-469d-486c-b6d2-e99c95f7dc5c
APIC (Attached picture): ()[, 3]: image/jpeg, 68288 bytes

The relevant entry here is: TXXX (User defined text information): (MusicBrainz Album Type). For the above four albums this tag is as follows:
 

• Anjunabeats, Volume 1 - TXXX (User defined text information): (MusicBrainz Album Type): album / compilation / dj-mix
  
• Armind: The Collected 12" Mixes, Volume 1 - TXXX (User defined text information): (MusicBrainz Album Type): album / compilation
  
• A State of Trance 2022 - TXXX (User defined text information): (MusicBrainz Album Type): album / compilation / dj-mix
  
• Hi-NRG Classix - TXXX (User defined text information): (MusicBrainz Album Type): album / compilation / dj-mix
  

This all comes  straight from MB via Picard, using the "Lookup in browser" feature. I'm using the proper ' / ' (space-slash-space) sequence to separate multiple fields within the same tag as per the recommendations; this has not been changed in advancedsettings.xml.

What I expected to happen:
Since all albums are tagged both as 'album' and 'compilation' they should show up both under 'Albums' and under 'Compilations' in the library, navigating as follows:
Home Screen -> Music -> Library -> Albums and Home Screen -> Music -> Library -> Compilations

What does happen:
All four albums appear under "Albums" as expected. However, only two albums (Armind: The Collected 12" Mixes, Volume 1 and Hi-NRG Classix) appear under "Compilations", in spite of the fact that all four albums are tagged as both album and compilation.

The Hi-NRG album is not tagged as dj-mix, but this seems irrelevant; two albums appear under 'Compilations', one tagged as dj-mix and one not.

In addition, only Armin van Buuren is displayed in the library under Roles -> All roles -> DJ-Mix which is also incorrect - Above & Beyond should be displayed here as well.

My question:
What causes this discrepancy, and how do I fix it?

All suggestions or pointers in the right direction would be greatly appreciated!!

// FvW

[MikeKL]

I was caught out recently over use of subtitle name for discs within a multi-disc Album not being visible and read correctly by Kodi Estuary GUI and found out that for this feature to work as expected my offending Mp3 files needed to be tagged with latest ID3v2.4 UTF8 tagging.
(I have updated both Picard and Mp3tag on Win PC to latest versions and ensured that tags for mp3 files are always written/updated to ID3v2.4 UTF8 from now on)

I know its not exactly the same issue as you have but perhaps checking/updating the tags of your offending mp3 files to ensure they are ID3v2.4 UTF8 will resolve your issue?

I am also using latest Nexus Nightly on an rpi4

[frankvw]

I'm about to do some further tests with that; I'll share the results here. I'm reluctant to think of this as a bug and reporting it as such, but once I'm done it should be clear(er) what's happening here.

[HeresJohnny]

Personally, I find that APEv2 tags cause less headaches. You can Kodi set to prefer APEv2 tags over id3v1/2 in MP3 via advancedsettings.

[frankvw]

I found it!

The albums that are listed under 'Compilations' have the 'Compilation (iTunes)' tag set to 1. The albums that are not listed under 'Compilations' don't.

So it looks like Kodi uses the 'Compilations (iTunes)' tag only and ignores the 'compilation' field in the 'release type' tag. Which is weird and warrants further discussion in a separate thread.

// FvW