Ive seen this a few times now and I’d really like to get to the bottom of it.
I do a lot of remote monitoring for clients and its very useful to have a Mikrotik on site for diagnosing issues for clients that have their own network. I setup a phone home VPN on the box and just give it either a fixed address agreed on with the netadmin or DHCP client.
On some sites with fancy corporate networks I run into a strange issue. If I setup the Mikrotik in the standard fashion with eth2 on a bridge, and bridge assigned an IP address either by DHCP or static, when I connect to the network everything on the switch I plugged the Mikrotik into goes off like the switch has detected some security issue 
Ive tried turning as many things off as I can think of thinking it might be some routing protocol it doesn’t like including mikrotik discovery etc, and whittled it down to just eth2+bridge with IP, and still takes the main switch down.
As an interim solution, I dont bother with the bridge just assign an IP to eth2, and then corp switch is happy. But I cant then do any bridging (sometime assign a port my end so I can effectively plug into their network).
Anyone come across this and can help me understand whats happening, and a solution?