I use Copernic on a dual display set: a 4k laptop coupled with a second screen. Whatever the resolution of the latter (tested two different brands: 1920 x 1080 and 3440 x 1440), the Copernic application is only displayed on this second display in low resolution (such as 1280 x 1024) whereas the resolution is normal when I move the window on the 4k laptop screen. This problem occurs only with the Copernic application.
I had a similar problem. High resolution center screen and two lower side screens. Once Copernic moved to center then tried to go back and the display size remained excessive. Solution was to turn off high res screen, reboot copernic on low and not to move it. The SW drivers should be fixed to solve problem.