Camera is powered trough the AC>DC external powerbrick located next to a camera itself. 15 meter long CAT6 UTP cable is running behind a drywall from router to the camera. If I connect this cable in any of the routerboard (using RB2011UiAS) Gigabit ports, port is flapping up/down every few seconds. If I connect this to the 100Mbit port of the router, it still flaps randomly every few minutes. My solution was to purchase the cheapest possible TP-Link 10Eur switch, and put it between the camera and router - port flapping problem gone.
What’s more funny is that today I encountered the same port flapping issue with another IP camera that I was setting up, and it was connected directly to router with a super short 30CM STP premium cable, so there is no interference involved at all, imho.
P.S. here is my original topic about this problem 5 years ago - http://forum.mikrotik.com/t/non-stop-port-flapping-on-rb2011uias-running-6-30-1/90049/1