HDMI to DisplayPort Not Working
I would go from your mini DisplayPort (mDP) to DisplayPort (DP) or go HDMI to HDMI from your MBP to BenQ.

The reason why is that DP (newer standard) supports HDMI (older) signaling quite easily through a passive adapter, while going from HDMI to DP requires active conversion.    This is probably the reason it's not working.

I have run into this problem before and what I have found to be reliable is to minimize (at worst) to eliminate (at best) the number of conversions you must do.  If your BenQ has a DP connection, I would use its companion technology, mDP to make my connection.