Thanks for the report, I was able to replicate this on macOS 10.15.7 with the current , using the shortcut when not editing the text of a note; also with the combinations of ⌥ with U, E, or N.
For the record, which version of macOS are you running?
The issue does seem to be resolved with the current Scapple beta, which you can download from here. If you’re running into the problem regularly, you might want to switch over to using that; there aren’t any major known issues with the latest bulid.