How to unzip split files on OS X
Google Takeout generates split zip files, without numberered file extensions.
Unzipping each individually results in most images not generated, with only the .json file for it.
Solution:
in Terminal, navigate to folder where the split zip files are and run:
unzip '*.zip' -d /path/to/unzip/destination
Source:
https://superuser.com/questions/365643/how-to-unzip-split-files-on-os-x