Hello !
Unfortunately, the problem known from old versions of RouterOS has returned. TL-WR841 cannot get IP from Mikrotik DHCP (still get defconf offering lease without success). Downgrade to 6.46.6 and everything is back to normal.
http://forum.mikrotik.com/t/dhcp-server-offering-lease-without-success/107119/1
Problematic configuration:
TL-WR841 ← WDS Client to MT → hAP ac^2