Hi... i have this strange issue with my serial monitor. When i open it, the window is opening in the taskbar, but not on screen. I cannot access it either... Who knows what it might be? It happens with 1.8.12 and 1.8.13.. So it might be a system (Windows 10) related issue, or a board issue?
Did you have an additional monitor connected in the past? In that case, it's probably on there