Running Studio One Professional 5.4.0.66465 on Windows 10 20H2.
Step 1: Right-click on any Event, it can be Instrument or Audio.
Step 2: At the bottom of this menu list, hover over Event, Audio, or Instrument Parts.
Step 3: Notice how the new panels open up when hovered? Well, once any of the three panels are opened, click on Event, Audio, or Instrument Parts again. I mean, actually click on the buttons rather than just hovering over them. Quirky habit of mine I know, but I guess that's how I discovered it!
Step 4: Whoops! All three of these menus are not only all opened at once, but are stuck -- and unlike how these sorts of menus normally behave, you can only close them by selecting one of the options, which then requires an undo.
Running Studio One Professional 5.4.0.66465 on Windows 10 20H2.
I'll be happy to provide any other details, especially if the error can't be reproduced on other systems.