I.e. instead of one scrollable view that lists both the unclustered as clustered tree, split this view into 2 views one for unclustered files and one for clustered files each with their own scrollbar

Sometimes clustering just doesn’t work correctly, not sure why, maybe because of white space issues in the tags. So my workflow was to first find a release for the cluster, then check the unclustered file list for files that maybe should be added to the release. If you have a long list of files, then that currently involves a lot of scrolling up and down. With two separate views you can keep the scroll position for both unclustered files as clustered files on the same position (i.e. at artists starting with the letter A)

For background see https://community.metabrainz.org/t/feature-suggestions-after-matching-a-huge-messed-up-folder/712286