This sounds like gzip is silently failing when it runs out of space. How large is your instance's EBS volume / local disk that you're unzipping onto? (run df -h
and figure out which device you're unzipping in.)
Additionally you could try to run gzip in verbose mode to catch any errors it might not be showing. I don't have a CentOS machine handy, but you might be able to use gzip -l [filename]
to figure out whether your file is too big for the target directory.