Different Sized Images In PDF

I have 13 PNG files that need to be combined into one PDF file however when I do this some end up small and some end up big. I didn't have this problem in the past but now I do. I checked the file sizes and they appear to all be the same (6096x8382 px).

6096 x 8382 pixels

Bit depth: 32

The files vary in size at around 40-50mb.

I did find an option to do a further Print to PDF and resize them but this seemed to affect the quality. I don't get why this is a problem now when it hasn't been in the past. I thought maybe the files themselves were different sizes however they all seem to be the same size?