I’ve the most recent W10 Pro update 1803 (April Creators) and it’s fine here, but I’m not using the most recent Shotcut version due to the many other bugs introduced with keyframes, so if you don’t need keyframes at the moment, downgrade to the previous version and see how that goes.
If this was fixed way back in version 18, it appears to be broken again in the latest version of Shotcut. I have version 19.07.15 installed on my machine, and scrub audio enabled. However, scrub audio is not working using the arrow buttons or by dragging the play head slowly across a clip. I have exited and restarted Shotcut several times and rebooted the machine, both to no avail. Is there anything else I might try?
That is bizarre since I am currently working with an audio track and scrubbing works with the arrow keys. And I use version 19.07.15 as well.
Could you try the portable version? Perhaps your installed version has some issues.