I've had something similar occur. I hadn't used my Lotus in a while but have recently returned to using it daily and noticed that the vapor production among my three caps was inconsistent. All the plates were quite dimpled and scorched. I had a hot plate replacement so I replaced the one in my newest vapor cap. That seemed to make a big difference. But I don't really see why it would, since the plates, while obviously used, weren't cracked or punctured. The thermodynamics of the vape are pretty simple — no moving parts, electrical connections , or inaccessible components.
So, now that I've been using the Lotus daily again I figured I'd re-try them all. The newest one, with the new plate, worked perfectly and the second oldest one worked okay as well. I noticed that the second hit was always better than the first, and I think that may be because my newly-harvested weed isn't as dry as it will be in another week or two. And I also think that my torch technique may have improved with practice. But the oldest vapor cap still seems to have limited vape production compared to the others. And it also smells like scorched wood. I may take it apart today and just see if there's some debris in there.