We recently upgraded from Qt 5.6 to the latest Qt and observed very high CPU usage (100% of a single core) by our QTableWidgets. We tracked this down to the scroll bars being present or not. When the table widget is made small enough that both horizontal and vertical scrollbars are needed, CPU usage hits 100%. When just one scrollbar is active, it does not display this behavior. A user does not need to be scrolling to hit high CPU usage. Just having the scrollbars shown is enough to get high CPU usage.
This behavior is not present on Qt 5.6, but is with Qt 5.13.2 on both Windows using mingw 7.3 64 bit and on Centos 7 using 64 bit GCC.
Please refer to the attached example to see the issue.