My Duplicati isn’t in the mood for rebuilding index files. When yours get rebuilt, what’s in the list folder?
Having no list folder seems to be the normal thing if there are no blocklists around for multiple-block files.
By the way, I put a technical explanation for one all-dblock download cause into one of your articles here. Possibly your workaround fixes a VolumeID of -1 somehow? You’d need to look for it in Block table to see.