I haven't seen anything like this, and i use a similar setup as yours (including the constant connect/disconnect of the external monitor).
I have one doubt, though: does farr show on the taskbar but not on the screen?
One possible explanation might be that the last time you closed farr, it was on the external monitor, and when you disconnected it, you can't see it anymore.
Another question: do you set the external monitor as the primary monitor? Is it larger (in terms of pixels) than the internal monitor?
If you'd like, i could code something really fast that would allow you to bring any window to the center of the monitor.