I think it is probably your herb that is the culprit. I've noticed the same thing. The cannabis that I have problems with looks like really high quality too, but it just doesn't produce as much vapor. I've seen amazing looking cannabis in dispensaries that was lab tested at only 6% THC, so you can't go on looks alone. I usually get very high quality myself but sometimes I get a lower quality batch too. It just so happens I got lower quality right as I got my Grasshopper, good thing I saved a quarter of the last stuff. The better stuff definitely produces more hits with thicker vapor.
When you combust you will get roughly the same amount of smoke no matter the quality of your cannabis. Most of what you are burning is cellulose. With vapor you are only extracting the active particles, so if the cannabis is less potent you will have less vapor, no matter what. I can get literally 2-3 times as many hits out of really high quality material vs lower quality. And when I say lower quality I don't mean schwag or mids.
I know common wisdom is that drier material vapes better. I personally think moisture is not a big deal. In my experience it just takes an extra hit or two to dry it out and then it produces vapor like normal. Perhaps it's just that my vaporizers are more powerful. I'm not sure how wet cannabis would have worked in my old iolite for example. But especially in a convection vape moisture of material should not reduce the overall vapor output. If moisture is a problem simply leave your material exposed to air until it's at your desired moisture level. Maybe as a test grind up a small amount and leave it out on a table to dry for a while before you vape it. See if that produces more vapor.