mergeFolderAlbums=true not merging composer-split albums despite matching Album/Album

[jdm]

I have spent more than 2 hours trying to solve this issue with Claude. Here is the problem.
I'm running MinimServer 2.2 on a Synology DS214Play, with a classical music library organized by composer (one top-level folder per composer, e.g. Y:\Lambert\, Y:\Couperin\, etc.). This causes a general problem: whenever a single CD is an anthology spanning multiple composers, its tracks end up scattered across multiple composer folders, and MinimServer shows it as several separate albums instead of one.

One example (among several in my library): "Airs de cour du 17ème français" (René Jacobs / Concerto Vocale) has its tracks spread across 13 different composer folders, since the disc anthologizes works by 13 composers. Browsing by album on my control point (BubbleUPnP on Android or Luminplayer) shows 13 separate album entries, each with identical cover art, instead of a single merged album.

I've set mergeFolderAlbums=true (confirmed via Properties > Server tab in the web config, showing true), and also set startupScan=full to rule out a stale cache, then did a full Restart + Rescan. The split persists.

For this example, I've verified the following, both via Mp3tag (selecting all 13 tracks across the composer folders at once and checking that fields don't show blank/multiple-values) and via a writeAllTags dump:

ALBUM is identical across all 13 tracks: Airs de cour du 17ème français (confirmed as a single distinct value in the writeAllTags output)
ALBUMARTIST is identical: Jacobs (also a single distinct value in the writeAllTags output)
ARTIST is identical across the visible tracks in Mp3tag: René Jacobs, Concerto Vocale
DISCNUMBER is 1 on all 13 tracks
No folder name match filters (no ['...'] suffixes) on any of the composer folders
No DISCSUBTITLE tags, no [part] in any folder name

As far as I can tell from the documented merge conditions (matching Album name, matching AlbumArtist, matching folder filter), this should merge — but it isn't, and this same pattern repeats across other multi-composer anthologies in my library, not just this one disc. Is there something about composer-per-folder library structures specifically that interferes with mergeFolderAlbums, or some other condition not covered in the user guide? Happy to share the relevant lines from the writeAllTags output or a Debug/Trace-level log excerpt if that would help pin it down.

Thanks in advance.