After a long and mysterious journey, the SBD I transferred to Polo just before the HF have finally arrived in my wallet!
The ticket I opened about this is still "being processed", though.
I dare not hope they have finally fixed things, but you may want to check to see if yours have arrived as well.
I will now transfer said SBD to Bittrex.
Edit: transferring the SBD to Bittrex worked as well!
Photo by me