Thanks Geo for explaining that.
This is a known issue and one been working to fix, thought I had fixed it BUT it still occurs with some comics.
Basically whenever you add a file to a zip/rar file it gets given an index number. So first file added is index id 0, next file 1 etc.
I think I might have fixed this for .cbr/rar files but seems need to do some more work with zip/cbz files. My function basically opens the cbz/cbr file, finds index numbers then sorts them by filename.... but I'm guessing still few bugs in code.
Also reason cover thumbnail random page is because the extract thumbnail script that runs in background also based on my comic preview code for opening zip/rar files so it see's that page as first page so extracts it, resizes it and puts it in thumbnail folder.