I found an interesting and serious issue about wireless interface configuration on RB751U-2HnD.
After every power cycle, the router stop the boot process due to the wifi network initialization failure (I believe): the green wifi led doesn't switch on. As side effect, the router eth1 interface is completely unreachable: no wifi, no ping, no ssh, no winbox, no network connection!
I'm using RouterOS 5.14 and firmware 2.38. I configured the wifi to use 802.11 2GHZ B/G/N band (with 2GHz N the problem it's the same). If I configure the wifi card to use 2GHz B band then after 4 or 5 _quickly_ power off and power on cycles the board start working again.
In the log files I didn't find anything. I tried to use the same router configuration on a second RB751U-2HnD but the problem is the same. So I think it isn't an hardware issue.
I opened a Mikrotik support request [Ticket#2012040466000027]: I'll give you any feedback from this channel.
Does someone experienced the same issue?