I got 2 of the mentioned routers. When I enable wlan adapter, the router becomes unstable, slow, and it hangs after few seconds. When wlan is disabled, the board works fine.

I installed ROS 6.7 and upgraded to 3.10 firmware. Both of the routers came from the same batch and had problems out of the box. Other boards work normally.

Any ideas?

EDIT: I tried the ROS 6.8RC1, the issue remains.

How have you configured the router board?

Are you using the original power supply?

Mikrotik support found the problem source: the issue happens when the antenna cable (the cable that connects onboard wifi and the omni antenna) goes over the PCB. So, if you move the cable aside the PCB, the board works fine. Go figure...

Ok, great, thats mean that the Wi-Fi signal disturbed the router board?
Good luck

I know that isn't very comforting, but it realy works ok. We performed numerous tests and torchured the board and it behaved ok.

I can confirm the same problem and confirm that solution, mentioned by tnakir, works.
Disassembled the router, moved both antenna cables away from the board and (just in case) glued them to the case with glue gun, so they can't go back and touch the microchips. After that wifi speedtests jumped from 1-2 Mbits/s to more than 30 Mbits/s and router passed two hour stability download test without problems.

Thanks, tnakir!

After Hours of searching slow wifi , i found this thread, and i opened my MK router and put aside the cables , now i can get 24mb download , before i was maxing out at 5 to 10 mb depend how far i am ,

still i have 20 mb to find out how to get them,

thanks for this hint , it helped me a lot, i never knew MK are so bad in design.