maybe you're just not vaping exclusively enough, I've been a mixed vaporst-combuster for a long time, since I was never a big combuster, and started vaping for the high, so I didn't have a strong incentive to stop combusting once in a while(mostly as variation, when I wanted a different effect, or just got an urge to combust)
this shifted towards only combusting when I'm with friends, or a situation where vaping is too inconvenient(festival, some parties etc).
but this summer I have had a period of a few weeks where I haven't really hung out with friends(we have a regular bar and I'm used to just going to the bar and always meeting people there, but lately a part of my friends is going to another bar more, wich I didn't know yet, so I kept meeting no one the times I went to the city)
and now combusting barely gets me high, wich I discovered during a session with a friend who had been away in the summer, he hadn't smoked for a frew weeks(and already is morecsensitive to weed, alcohol etc usually), so after a joint he was really high, I just noticed a slight effect(and a slight headache-like feeling). loaded a bowl in my VG, wich was much less as what went into the joint but lasted a lot longer, and that got me much higher as that joint.
so now I'm switching to vapor around friends too, mostly because of that period of a few weeks exclusive vaporisation