If you clean out the firebox completely. All the pellets will be removed.
If you try to ignite the firepot with no pellets, it will take a few minutes for the auger to push enough pellets into the pot for the fire to ignite. It sounds like that is what occurred after your maintenance.
There is a Auger Prime feature that can be used to push a few pellets into the pot before you push the ignite button. There is a recent thread that discusses priming the auger. Some are like me and always prime the auger before every cook. Some only prime the auger after they clean the fire pot. Other have never used the priming feature. I cannot tell you which procedure is right; I only know what works for me.
Although Traeger says to ignite the fire with the lid closed, I always leave mine open until I start to see some smoke pouring out. Then I lower the lid. Again, I can't tell you if my method is the right one, but it works for me.
The one thing you should never do is try to reignite a fire after a flameout or if the grill does not go through the normal shutdown routine. If the pot is full of pellets and you try to ignite the fire with the lid down, sufficient hot gases can build up in the chamber to cause an explosion. If the grill does not go through a normal shutdown, be sure to clean out all pellets from the firepot before reigniting the grill.