Menu editor completely hangs site

I created a new admin menu.
Some kind of race condition exists where each click of “add menu item” takes 15 seconds or more to complete, and then everything hangs anyway.

I’ll get the drag/mopve cursor when hovering on any menu item and the drop down arrows on the menu item boxes won’t work. Only way to recover is to deactivate plugin. I’ve tried to install and uninstall twice. Same issue. I assume there must be a bad bug or a conflict. Are there known conflicts with other plugs I might investigate? I just don’t have time to deactivate and add in one at a time to debug one plugin. Any ideas appreciated