I would say that if your gun fires better with loose powder that you don't have a good spark path. (loose powder can get farther up if you do have a devious spark path).

Finicky muzzleloader weapons have often been known to prefer loose over pellets. I do think it's because in the case of a marginal spark path the loose powder gets closer. I've never seen or heard of a muzzleloader weapon that preferred pellets from an ease of firing standpoint. But a well tuned one should shoot pellets easily (all 4 of mine do).

Even if you do have a hard time getting it to go off the first time, it certainly is dry after that and should fire right up (loose or pellets) with the next load.

Since it doesn't, I say yor spark path must be the problem. Can you remove the striker and look thru the barrel towards a light? If so, do you see a nice clear spark path?

I've decided that it absolutely must be the spark path.... unless its something else.

I'll be curious to hear about how a patch looks after firing a cap, and also if you can see a good clear spark path.

Good luck!