Mixed DPI still doesn't work reliably for me on Windows. Lately mine has been confused with dragging windows between monitors, they'll get stuck on the border when dragging even though I can move my cursor across fine when not dragging anything.
It could be unrelated to the mixed DPI scaling, but that's what nearly all my display issues on Windows have been related to so that's my assumption.
Windows occasionally "stick" a bit when dragging between windows monitors even with the same scaling on both screens. There are a bunch of keyboard shortcuts that are very reliable though. Windows Key + Shift + Direction: left/right instantly moves windows between displays, up maximizes, down un-maximizes and then minimizes. Windows Key + left/right (so without shift) also docks windows to the left or right of the same screen, and this feature is what makes windows also "stick" when dragging them from one screen to another.
I also recommend you check your display settings. If your windows aren't the same vertical size, then your overall desktop isn't a rectangle, it'll be some other polygon, and that means there are corners between the screens that your mouse can get stuck in.
It could be unrelated to the mixed DPI scaling, but that's what nearly all my display issues on Windows have been related to so that's my assumption.