Seems like the USB port shuts off as soon as 100 mA or even less is drawn from one of the USB ports.
So the Pi continues to work but the USB device loses power.
Quite sure the dongles use more power than that.
See this video, Dave from EEVBlog is testing the device:
Temporarily I hope as I am eying PoE as well. The problem has been identified, a solution will follow: PoE HAT - USB Ports not working - over-current (FIXED - New Hardware Release) - Page 5 - Raspberry Pi Forums
This was workaround for C.H.I.P. board
I am planning to try those on my remote installation (inject 12V):
https://www.amazon.com/BeElion-Passive-Injector-Splitter-Connector/dp/B01HMNJHII
With this stabilizer (I actually bought the 3A one, 8V-40V) :