Hi,
I tested my Woobm with a bunch of hexS. Via PoE or direct power.
The Woobm flashes in random order and show up sometimes as AP, sometimes not. A successful connection was not able. Reset was done → no effect.
The Woobm works with my other RBs as intended.
Is there problem a with the combination Woobm + hexS??
The hexS are all ROSv7.5.
MT says (please note the “any” part):
Simply plug it into any RouterBOARD USB port […]
Might be related
http://forum.mikrotik.com/t/routeros-7-5-where-is-ups/161198/1
USB detection in 7.5 is a problem
Good point, the other RBs are not ROSv7.5!
you could create your own ticket @support and link to this thread 
Hey, were you able to solve this issue? I have 5 woobm and all show that behaviour, even when i plug them into a linux box or even an usb charger (so for me it is not ros related). Could you please test if AP stays available (sends beacons/led flashes) if you connect a woob to an usb charger/power supply?
my woobm attached to a poweradapter. showing up as an AP, looks fine.
And NO, the issue is NOT solved, the bug is NOT fixed. ROS 7.5+ has problems with USB as confirmed by techsupport.