I've had this issue, intermittently, where applications on my second monitor will show behind the DF taskbar. Initially, this was noticed when I started using Start11, which I have since uninstalled. Their have been instances where I did not experience this issue, and then the issue crops back up again.

I have contacted support in the past, and they said it was a Start11 issue, and I thought the issue would fix itself, after I uninstalled the application.

Interestingly, I started my computer, without logging in, for quite a while. I logged in and the Start Menu was working appropriately. I thought this was weird, so I did a restart, and the start menu is back to acting up as I described. It seems like something just isn't hooking correctly.

Same thing happens for me. Task bar seems to play nice for a while, then I notice maximized windows have slipped behind the DF Taskbars (or the DF taskbars are in front of the windows??).

As @Owen is there a fix in the works? I just enabled the turn on "Enable Prompt to Restart Explorer when Issue Detected" and will keep an eye on the issue. LMK if you need more debug info.

I enabled that restart flag in advanced settings restarted DF, and that didn't do anything initially. Then after about a minute, it prompted to restart WinExplorer b/c couldn't reserve space for taskbar. FWIW, I don't have Start11 installed, but I do use Open-Shell Menu (v4.4.191)??

Since I enabled "Enable Prompt to Restart Explorer when Issue Detected", I have not noticed the issue happening again.