(C++) When trying to read files, getting an error that says corrupted size vs. prev_size

This is what my Read File method looks like

This is what my terminal shows with the error after attempting to read file

This is how it should look like after successfully reading in a file

The error seems to be where the program cannot read in a test file where the x or y axis goes above 8. Therefore some test cases are readeable whereas others with larger axis' will show an error which says corrupted size vs. prev_size. Please help!