XnView Software

XnView MP 0.99.4 x64 (zip)
Windows 10 Pro
Monitor: 3840x2160, 150% scale

Double click to open the file.
Image is scaled (99.x%). see display1.png.
First zoom in and then zoom out and the display will ok. see display2.png

Thanks to your detailed description I can reproduce the problem.

This problem is supposed to be fixed in XnView MP 0.99.7. Please check and confirm the bug fix here.

Confirmed, it is fixed. Thanks!