It's not the Cybersyncs or the flash unit, but the inherent design of the PC port. Photographers have been dealing with the problem of loose PC sync cables since the PC port first came out. There has been an attempt to improve it by introducing the screw lock PC port, but this is still a PC port and prone to the sync cables plug becoming opening up over time with use. It looks like flash units are now slowly getting away (alas its a very slow process) from the PC port. Another downside it that every PC cords plug has different initial tolerances for the opening. A better choice for the sync port would be a 3.5mm mono-plug port or even a 2.5mm mono-plug port, you dont have to worry about the sync cables plug opening up for a looser fit, since the plug is a solid piece.
Also unfortunately while PCunite has the right idea of putting a mono-plug port into the flash, him having receiver being only supported by the sync adapter is a bad idea, it is putting extra strain on both the receiver and the sync port on the flash. In this configuration, you run a higher risk of seriously damaging either the flash or the receiver if they were to get knocked to the ground, then if you had the receiver being attached by a cable and either hanging via a lanyard or attached to the flash or swivel mount/lightstand via either velcro or even an elastic tie. If the flash where to hit the ground receiver first the force of the impact would be transferred to the sync port on the flash due to the rigidity of the connector, where as with a cable, the force of impact would be mostly absorbed by the cable due to its flexibility