I have 3 CSS326-24G-2S+ switches connected to each other - one by 10Gb DAC and the other connected by 1Gb fiber. All three switches have active lan ports flashing at the same time. I had to do a reset on each one because they would hang and freeze up ports previously. I downgraded to firmware 2.3 and they are working ok now but the lights keep flashing. Wireshark on the network shows no broadcast storm or excessive activity. Is there something else wrong with the switches to make them flash port lights like this?
Switch by default sends out periodic (every 2s) RSTP BPDU packets, you see these flashes probably due to this reason. You can try to disable RSTP at some 1Gbps port and see if flashing stops.