Ok, this is a long shot, but it happened to me about 4 months ago. Each RJ45 male end has 8 contacts and each contact is separated by plastic ridges. When you plug the RJ45 into the female plug (ok the socket end for you gender-phobic) the 8 wire "fingers" need to drop between the plastic ridges in order to contact the metal on the RJ45. (see the attached picture)
In some Asante switches I was using, the 8 metal "fingers" in the RJ45 sockets were just a little bit too wide for the clearance in the male plug. Some of the fingers just couldn't quite drop into the slots. After wiggling (is that a technical term?) it for a bit, they would work themselves into the slots and everything would be ok. I suspect either the finger dimensions were out of spec or the slots on the RJ45 ends were out of spec, but to this day I don't know which.