I faced same issue , installed Mikrotik HAP AC2 in room 1 , room 2 , with one wall in between and 8 m away, no signal. Opened the box , relatively easy to open, found the two antenna connections , fitted external antenna from an older router and yes ! 100 mbps at the router , thats the provider spe...

Thanks! I am in Taipei now, will try to find these connectors today.

I know it is an old thread, but have you able to successfully connect external antennas to the board?