I had some time to play around with it. I think I've got a work around, but I'm not sure how permanent it is.
If I change to any display resolution while the bar is not in auto-hide mode, the full bar appears and stay on screen without issue. If I then switch it to auto-hide mode then the bar breaks again as in the previous image.
If I first change to auto-hide mode, and then switch to any resolution (including switching back to my original resolution), the full bar is shown and even auto hides and reappears as expected.
What's interesting is that I had the bar in auto-hide mode when the system was upgraded to Windows 11. So flipping the resolution back and forth after the upgrade seems to fix things. I'm not sure if a system restart, power down, log out, etc. will re-trigger the issue though. I didn't test those out scenarios but hopefully that's enough to go on to figure out/fix the issue permanently.
Thanks for your help. The workaround is a great first step.