I doubt drop is from gpu, most likely cloud.
Big cloud miners tend to mine new coins at the coin beginning and not stay for long. There is few newer cpu coins so maybe they moved further.
I thought ZETTEL coin is a CPU efficient and it's faster than GPU.
From what I understand, ZETTEL is GPU and pool resistant... both _could_ be implemented. At this point, I believe the consensus is to remain CPU only for now. The Dev would be able to give a much clearer picture, but I think he's heads-down, working on the modified algo mentioned a few posts earlier.
Great.