I am running 12.17.5 Beta and this toolbar stays above my taskbar even after closing Opus. I am not able to click on or delete this either. Any help or advice with this would be much appreciated.
Looks like the same issue as this:
Yes sir. Sorry I didn't notice that user's previous reporting of the issue in a prior version
That's no problem. 
There are some things to try in that thread (GPU drivers and a settings change). Please let us know which (if any) make a difference. We're also looking into what changed to see if we can understand why it's happening on some machines but only 2 so far.
There are some changes in Directory Opus 12.17.6 (Beta) which we hope will stop this happening.
Please give it a try, with transition animations turned back on, and let us know if the problem is gone or still there.