hi dougr
(paragraphs are you friend here 
)
You don’t say if you are on windows or OSX but yes there are some multi monitor issues, in windows at least.
The fix for missing or corrupted GUI (as you found) is to open on your PRIMARY monitor and then drag across to your 2nd/3rd monitor and they will continue to work. FWIW The affects all 3 vst connect plugins not just the main one.