It is definitely related to the stardock software (Start10 and/or Curtains), as the problem will go away when I uninstall one of them.
For reference, see my first post in this thread (I've also posted the blur).
And from the video it looks like you as well have the wrong blur? This is not the acrylic blur that is windows's standard. You can see how it looks different in the preview window of Start10 (where it shows the acryl blur) but your actual taskbar has the normal blur. I'd be curious if you uninstalled Start10 if you'd have the acrylic blur again?
Again, see my screenshot at the top for reference (difference between acrylic and "old" standard blur)
I'm really confused about this issue
Setting the transparency of the taskbar to "BLUR" in curtains fixed the problem for now. That fix didnt work last time though so either something on my machine is broken or there is a bug? No idea, anyway, for now the problem is resolved once again...