problems with Artist.displayFormat

[stefano_mbp]

Just simulated your setup.
Artist is Festival Quartet
Composer is Johannes Brahms (1833-1897)
Artist.displayFormat={$artist$composer}
Flac file, don’t have any mp3
On Lumïn app control point the result is (in red)
.
As you can see it works as expected, I think something is wrong in your file, maybe tag version or something else
.