Slow QScrollBar on Windows. How to be?

Question

Qt

I am making a graphical application where the speed of processing records plays a significant role. The essence of the program is to read a binary file and display it on the screen. There can be any number of entries. Well, somewhere on average 100MB of a file ~ 2 million lines in a table in the application.
Made caching of records and displaying in the table only 200 pieces. In the model, RowCount() = 200. (When scrolling, the necessary records are loaded, and so on)
QscrollBar freezes on Windows. On Linux (ubuntu 16.04 on vmware) there are no subvisons. Everything is going so smoothly that you can't even believe it. The same code here and there. And I read the same file... I
ran it with debugging and without debugging. Equally

Answer 1

And in which widget do you put the lines for display? Maybe it's not the scrollbar that slows down, but the problem with the scrollbar?