Did you changed the screen percentage (f.e. via post process) for your renders, or the render resolution? Or both at the same time?
Keep in mind, that an increase of the screen percentage of 200% (or factor 2 in HighResScreenshot) will not double the rendered area, it will quadruple it -> 2 times the lenght of the original resolution + 2 times the height of the original resolution = 4 times total area of the original picture. If you have this active, while also increasing your resolution to double the original size, the rendered area just skyrockets.
resolution 1920x1080 + 100% screen percentage = size of 1 original picture
res 1920x1080 + 200% screen percentage = 3840x2160 = size of 4 original pictures
res 3840x2160 + 100% screen percentage = 3840x2160 = size of 4 original pictures
res 3840x2160 + 200% screen percentage = 7680x4320 = size of 16 original pictures