Occasionally doesn't recognize a computer and ends up just charging

Sometimes it immediately gives me the Do not disconnect symbol and syncs fine with the computer. Other times it waits for a while and just charges. It works just fine aside from that slight issue, hard drive and battery are still good aswell.

I have no idea about the pattern where this happens - this issue has been happening with the same cables and same computers. I’ve restored it 3 times already. This also happens when the iPod is in disk mode - occasionally it will connect, other times it’ll just charge.

What could be possibly causing this?