All,
I’m currently on 12.9.0.14
In the Project Manager pane, I selected a list of schemas, right_clicked, then selected Editor to open multiple editor windows.
Toad went into a wait for a few secodns, then nothing happened 
Is this a fixable issue?
Ok,
I gave t another trywith just three schemas selected. That works - more or less.
Toad goes into wait, establishes a connection, goes blank, is reported by Winodws as not responding, but Toad perseveres, and, ultimately, comes back to life with all three sessions established.
I can imagine that opening multiple sessions may take some time, yet the behaviour is a bit awkward. How about a little pop-up showing progress?
Some of the intermediate stages should be avoidable, imho, such as going blank and/or not tresponsive to the OS.
Just some thoughts…