Missing files inside synced zip files

I'd just leave it unfortunately. You could contact Microsoft to let them know about this if you wish, though since you know that another app works fine, it's best to continue using that app.

In general for all OSes, the built-in apps for mail, zip viewer, image previewer and so on, while effective for most purposes, might not work in all situations.

This is why we have paid and free software that has a specialist purpose, one for zipping, video playback, photo viewer, file transfer, etc. These tools are usually more powerful and can handle much more 'variables' than the OS version (since naturally, the operation of the entire computer, the sole purpose of an OS, is more important than making sure a zip file opens well).

Glad to hear that you managed to fix it on your own though! Have a great end of the week!