Sometimes, even though it was the same species of wood, where it grew and the condition under which it grew could affect burn rate. It may have been regrowth wood, that would be less dense.
I tend to agree with Bludawg though, you might just have been too late adding that extra wood, and lost the coals. And yes, everyone has bad cooks from time to time
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."