I posted a similar problem with the reconcile window in that t takes up too much space and I have to resize it and it doesn't remember the resizing for next time. In my case I resize to a smaller box so I can check my banks web page. I have noticed that I can't make it as small as 2017 as far as I remember.
Sounds like the same issue, though in the 2017 version I never kept it at it's opening size; I always dragged it to one size and relied on Windows to auto size it to fill exactly half of the screen, which it did easily.
And whilst I don't want my bank's website open as well, I do want a pdf of the latest statement from the bank open at the same time, so same principle.
In the 2019 release, do you find that at its smallest, the reconcile window takes the majority of the screen width, making looking at a second window difficult?