It's handled much larger files than that, so if it's something you don't mind sharing, you can send the file at https://www.moderncsv.com/report-a-bug. It is a beta version, so I'm trying to fix all these issues now.

Edit: On second thought, it's probably grayscale intensity hex values of a 1920x1080 image. I can reproduce that myself. Feel free to send me your file if you want, but it might not be necessary.