Yeah, yawning is ok. they have to stretch that jaw just like we do. Hm. Yeah, it could be some settling issues. Especially if he is a young one. Just keep trying. I have two little hatchlings (well, they are about a month old now), they have been pretty picky as well.

If he is young, you can feed ever 5 days until he is about 500 grams. You should see if you can't weigh him. Then you know if he is getting 10% of his body weight. It's hard with the little ones though. At least he is eating, so I wouldn't worry about him.