Just wanted to post that I ordered 3 Netmetal 5’s, 921’s, and one wouldn’t power on, tried with the other radio, same poe and adaptor and cable, same thing. Green light was on on the POE injector, power verified at plug. Tried new cat 5 wire, these were only 2 meters long for bench test reasons. Tried many things.
Turned out that the POE injector didn’t actually power the device, even though the green light was on.
Thankfully I killed at sxt5AC a while back and had the left over poe injector from it. 
so I used that.
Just wanted to post in case it becomes an issue with other people seeing green light but not power on the devices. out of the now 19 or so mikrotik devices I have in my home lan currently, that was the first ever in 10 years I have had an issue. So not bad. and yes, I have a somewhat large home personal network, that seems to grow every year to a new property to share internet 