Upgraded recently to version 12.18. Also had to change my admin account password to 20 characters. Appears I can start DOpus with the "run as" so I can have access to folders and files that are restricted to admin credentials. Although DOpus starts, it does not seem to pass along the credentials anymore. Each access results in the Windows dialog pop-up requesting my admin user name and password. Once I enter it, I have access. I cannot change my password to less than 20 characters because of group policy.
Sounds like Opus is already running in the background normally and when you run it again it just tells the existing instance to open a new window.
You can use File > Exit Directory Opus to tell it to quit.
But, outside special situations where there's no alternative, you should generally use the Admin Mode button on the toolbar if you need to do lots of elevated actions and don't want multiple UAC prompts. Launching the whole program elevated instead will break things by making unelevated apps unable to talk to Opus: