Welcome to the club. ARM and NV2 is not working well. Nstreme have the same problem.
http://forum.mikrotik.com/t/arm-devices-and-nv2-protocol/120717/1
Only thing which works is 802.11. Mikrotik does not solve this problem 
. To be sure, he does not even comment.
It is very sad that in end of 2018 we need to use only 802.11 on new hardware. NV2 and Nstreme are slow and unusable.