I couldn't reproduce this in Qt 6, so this is probably Qt 5 only issue.

This seems to happen only if WA_TranslucentBackground is set for frameless window.

To reproduce:

• 2 monitors, set primary at 125% and secondary at 150% scale (this seems to work best)
• run the example
• grab the window and move it between the screens multiple times (faster better)

The window randomly starts to change size. Sometimes it reverts back to the previous size, but often it just becomes ever smaller or larger.

It looks like when this happens there are is WM_SIZE event followed by QWindow::screenChanged(), another WM_SIZE followed by another screenChanged() call. After this there are Qt resize events being handled.