I experienced something similar my first day with my APW3++ and my D3.  For me, the fix was to unplug the PSU Power cord and leave it off for a couple minutes after the PSU fans quit running. (About 2 minutes or so for me)  Once I powered it back on, that seemed to reset everything to normal.

Marek, while running the Advanced IP Scanner, did you push the "IP Report" button next to the network jack on the Antminer? 

As someone brand new to cryptomining and especially DASH mining, I'm trying to understand the frequency for blocks being discovered.  Now that it looks like we are past the Orphaned Block issue, is it typical for the pool to go 12 hours or more between blocks?  I think the block count (https://chainz.cryptoid.info/dash/) is about 250 new blocks since the last one here at poolmining.  (I am not complaining, I'm just trying to better understand how it works.)  Thank you!