I’ve got the same issue, except using hAP ac3 and Asus RT-AC56U. If I connect to a different AP (I.e. tether to my phone), it works like a charm. So there’s something that MT does, but for the life of me I can’t figure it out.
This topic gave me most hope http://forum.mikrotik.com/t/dhcp-lease-over-wireless-bridge-does-not-work-for-ethernet-clients/138721/1 but it’s a no-go. And unfortunately I’m just not “network-smart” enough to do proper digging/sniffing, so replying just to let you know you’re not alone with this issue and hopefully someone smarter than me can figure out what’s going on.