I think you might be hitting the same hang I was able to reproduce before. I am not able to reproduce it anymore with the recent changes, but the underlying cause is still there. It was just that refactoring and speed increases made it impossible for me to get into that scenario.
My hang was specifically in response to breaking current SQL execution and then waiting for it to complete. It also was only reproducible on my 11.2 database using a 19c or 21c client. Using a 12c or 18c client was OK. I don't know if this is a problem with the component we use for Oracle connectivity or if there is something incompatible with that client/db combo. I looked at the compatibility matrix in My Oracle Support (metalink) and didn't see any notes about it.
Please try using an 18c client and see if it behaves OK. You can also see the first paragraph in this post and try to do those steps as well. In my case I was able to reproduce the hang when trying to cancel a running query in the Editor when running using F9.