The Advanced Settings title and button overlap in the editor:
Adding a top margin to .crx-collapsible > button resolves the issue (but I don't know if that's the kind of fix you'd prefer).
I'm seeing this in Wagtail 7.1.1 with CRX 6. Changes to collapsible block settings were part of the upgrades for Wagtail 7.1, so maybe that's related.