Mysterious disconnects every 4 hours at specific times (e.g. 08:02, 12:02, 16:02 etc)
Right so turns out that the switch was recording a Syn Attack and shutting down the port for 60 seconds. The switches time was out so of course the attack didn't coincide.
The issue was / is caused by the spiceworks discovery scan. Since the syn attack settings are effectively causing a DOS I've switched them to report only mode.