As far back as January 2018 there were complaints about how roon handled arrangers:
The specific issue in that post seems to have been addressed, but there are still inconsistencies in how roon reports arrangers, in that they are now given a separate line under the track title in the track listing.
When the user clicks on the Now Playing window at the bottom of the screen, roon displays a large image of the album cover and some information about the track. Unfortunately, here roon lists the arranger as Composer (along with the actual composer).
From this “cover” screen the user can select the “Open Book” icon in the upper right corner to display track credits. Here the arranger is completely ignored, not listed at all even as Composer - though the actual composer is listed.
I think both of these should be fixed - it is important metadata that roon is either misreporting or not reporting at all.