I can tell you the sad workaround I use these days…
- Double click the nested block to edit it
- Click on the next level nested block
- Copy it and stop editing the nested block
- Paste the next level nested block so it becomes top level
- Move it to the side
- Start over from the top of this list on the pasted block until you’ve drilled down to the one you’re looking for.
It’s mindnumbingly annoying, but it avoids most issues with nested blocks that I’ve encountered over the years (this and this especially, though you still have to be careful with show/hide while editing blocks). 