Downloaded music not showing and Roon ARC crashing during track transitions offline (ref#6HLS2X)

This (covers either entirely missing or only displayed as small low-res images, when offline) has been an issue for years and reported many times before. Just a few quick examples out of many:

Many more can be found by starting from these search results

https://community.roonlabs.com/search?context=user&context_id=suedkiez&q=%40Suedkiez%20arc%20offline%20covers&skip_context=true