subnet communication lost after 5 minutes

Hi,
I am facing strange behavior of my network. Basically I have got Satel Integra 128wrl with ethm1-plus module Alarm system connected to my Mikrotik’s network.
The thing is that communication is fine for like 5 minutes after I plug in Ethernet cable, or pull down and up interface on my Mikrotik switch, and after that time magic is happening.
I’d say that interface might be damaged, but that communication issues happens only cross different subnets , over the same subnet communication is working like a charm 24/7.
It is a bit annoying especially when I want to redirect Satel’s module so I can connect via Internet to it.
My current configuration is:
Internet ↔ RB1100AHx4 <-VLAN’s-> CRS326-24G-2S+ ↔ SATEL.

Does anyone met such network behavior? Every other hardware connected to network is working fine.