Intermittent issues can be a big pain. Do you have a cable certifier? If not, take Tim up on his offer for help. Whenever another vendor is blaming their problems on my cable I test and print the cert.

Send a copy of the result to everyone concerned. When they see all the squiggly lines in the test parameters and the "Pass" icon in the upper corner of the test result it shuts them up every time.

I would certify the cable as it is; then I would re-terminate the connections and certify again. I guess you could have a poor punch resulting in intermittent connectivity?

Scott