That's definitely not right...I just spent about 1 hour to go through the Pit of Heresy solo flawless. No tricks here I'm not one of those guys doing only boss checkpoint. Feel free to check on Dungeon Report.
As you can see from that screenshot it gave me the emblem at the end however the counter says "[i]0 Pit of Heresy solo flawless runs[/i]" which is definitely not correct since it just gave me the emblem for that triumph.
What's wrong??
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It saying you have none means you did a boss checkpoint.