On the AntiVirus software: i use windows defender. (Bad news for most AV-Software producers: in several tests of renowned computer magazines i read recently, they didn’t fare better than the defender. )
On bluetooth: i wouldn’t be aware of any bluetooth component on my machine.
On the last comment: it’s true, as the free USB-port after removing the EyeX was a USB3 port, the 4c now is connected via a USB3 port. I might try switching up things (perhaps even plugging the device to the USB-hub next to my screen), and keep an eye on this. But as the problem is sporadic (i haven’t experienced it now for two days), it’s hard to confirm it as a cure, i can only switch and give feedback if the problem happens again.