Well i have very weird issue on RB3011UIAS.

Mikrotik pass traffic only for 40 seconds every 1 minute.
When I do a ping for example to google from mikrotik . 40 seconds pingable and 20 seconds not pingable. It is look like time slots of internet.
What is strange : In moment when i start Packet sniffer on WAN interface : Mikrotik magically start to work normally. until i press Stop in packet sniffer settings.
Any ideas what it can be ?

If I remember well, packet sniffing disables fasttracking in the firewall, so the machine starts behaving different.

So if you use fasttracking along with policy routing (routing-marks assigned in mangle), this could be an explanation of the weird behaviour, as fasttracking is incompatible with policy routing unless special measures are taken.

Also, I was solving a very similar issue recently at colleague's home network, and something in that network was not happy about RSTP protocol being active on the bridge.

Hi, Thanks for your answer.
I just checked firewall and i not see any fasttrack rules there.
I also checked WanBridge . It have STP : none.
So most probably issue somewhere else. May be another ideas ?
Well i fighting with this issue already month or so without any result.

Issue was due to Interfaces->Detect Internet feature. After complete disable this buggy and crap feature everything started to work.