I'd agree with that idea about making sure they're dry.
Someone else commented that the cherry pellets are much harder to keep lit, and they mix with other types.
I find that the smouldering
AMNPS takes a bit more airflow than you'd think, especially if there's any competition
for the oxygen inside the smoker.
My propane gas causes me airflow issues, because I think it creates rather a lot of CO2 inside the grill.
You may also be in an oxygen starved environment inside that smokebox if you're burning other wood or charcoal too.
If you're on electric (you said burner, so you may be), you may simply have an airflow problem and what air is inside the smoker
is good air, just not enough of it.
Assuming you're electric, I'd differentiate between the two possible problems:
Burn the
AMNPS sitting out in the open in a spot where it should get all the air it wants.
If it still won't burn, look at the pellets being slightly damp (not even visibly seems to matter)
If it burns fine or even just burns better in the open, look at airflow.