Workspace Bug Identified; Work-Around Found!!
If a user has customized workspaces and closes Premiere Pro completely, the next time they launch the program, two things will be wrong: two-screen setups will have all the windows collected onto one screen, and the custom workspaces they saved are replaced with all the default workspaces that come with Premiere (their own custom workspaces are moved to the Overflow menu). So, users need to reorganize their windows for dual screens as well as move their custom workspaces back to the main workspace menu each time they relaunch Premiere.
What causes it:
The cause that I have found is when a user deletes the Premiere Pro default workspaces that they don’t want (i.e. - Libraries, Learning, etc.). Once those are deleted and Premiere is closed, the application sort of freaks out that those defaults were removed, so it refreshes some of the settings to retrieve the default workspaces and place them back in the menu. But it also moves all of our custom workspaces to the Overflow, and resets all windows onto screen 1 (instead of keeping dual screen setup).
After you set up your window positions for each of your workspaces, and after you have saved your custom workspaces, DO NOT delete the workspaces that you no longer want / need. Simply move those unwanted, Premiere Pro default workspaces to the Overflow or Do No Show menu. Doing so will ensure that relaunching Premiere keeps your custom workspaces AND dual screen setups where you last left them, and the default workspaces that Premiere seems to want to keep, will remain in the hidden menus you placed them in.