The config export is not complete. But anyway: never add VLAN interface back to bridge as port. Instead you should be setting bridge pirt as tagged member of MGMT VLAN.
/interface bridge vlan
add bridge=bridge comment=LAN tagged=> bridge,> sfp-sfpplus4,ether10 > untagged=MGMT_NET > vlan-ids=900
And make sure you have vlan-filtering=yes set on bridge.
I suggest you to read these two tutorials, they will help you to better understand the way bridge and VLANs work in ROS:
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1
http://forum.mikrotik.com/t/routeros-bridge-mysteries-explained/147832/1