Sorry for the late answer, hope to get any help after the past month.
The problem is that in this case my mouse doesn't hit the very edge. Taskbar does not unhide when I hover area where it should be, but appears if I click on that zone, and only after I alt tab to any program. Some software use this area, like Zen browser for the search bar or Jetbrains IDEs. Even when I want to click on any title bar buttons (close, minimize) at every Windows app, the problem remains.
I'm not sure if there is any advantages of hidable taskbar if I can't use the space that I win with this feature enabled, so for me It's definitely a bug. Let me know if I get something wrong.