I have been trying to prepare a zip folder for upload but the files will not stay in numerical order - I can even see them getting disorganised during transfer. Any tips ?
The file naming for the individual pages needs to be consistent and according to alpha-numeric order. Problems arise frequently when things like 'page 1', 'page 2'....'page 10' get automatically resorted as 'page 1', 'page 10', 'page 2' (all ones come before twos). So, for numbering, you should use 01, 02, 03, etc for numbering.
Another area where people tend to get hung up is that they are inconsistent with their punctuation...along the lines of Target_Comic_pg01, Target Comics pg02, etc. Inconsistent uses of underlines, dashes or spaces will sometimes files to get out of sequence.
In general, if you have a zip utilility like Winzip or Win RAR, you can use it to look into the zip folder and see how the files sort on their own prior to renaming the file to a cbr or cbz, and fix any problems you might have.