Problems with Gbit ports

Hardware MikroTik hardware general
1

I have RB800 connected to:
ether1: PC (Dell) with Mikrotik RouterOS and Gbit ethernet
ether2: RB435G
ether3: RB411
few wireless interface

It works fine for about 6 months. From about 1-2 weeks periodically ether2 and ether3 hangs for 3-4 seconds. It happens every 30-300 seconds (not regularly). Ether2 and Ether3 hangs together. I tried many different ideas:

  1. I’ve replaced RB411 with RB433
  2. I’ve disable ether2
  3. I’ve disable ether3
  4. I’ve upgraded RouterOS from version 5.12 to 5.20
  5. I’ve changed ethernet speed - 10/100/1000
  6. I’ve disabled full duplex
  7. I’ve changed ethernet cables

Nothing help. Do you have any idea where is the problem? What else can I do?

Regards

Marcin D.