Hmmm that should have worked.
Is there any chance that what was billowing out was steam and that your pellets burned up quickly since they were sitting over the element area and may have burned up really fast and all at once? Then all you saw coming out was actually just steam. Steam and smoke look similar in many cases from a smoker.
If that isn't a possibility at all I would switch pellet brands and try 100% hickory and see what happens in that case.
I know that Pitboss Competition Blend is quite mild so if I smoke anything less than 5 hours with it I can light both ends of the
AMNPS and it works well.
These days I doctor up Pitboss CB by mixing more 100% hickory in it so I end up with about 65% hickory total. That does the trick for me without having to light both ends of the
AMNPS.
You may just have a weak pellet blend for a pork butt.