Nope, you're not being thick. I was baffled by that chart the moment I saw it. Seeing it again only compounds that.
The control in Treatment 1 appears to be driven by placebo, but if the sham had zero therapeutic effect, then after the washout/crossover period, I would (under ideal conditions) have expected the dB/SL of those now receiving the proper treatment to notch down to around -5 dB by about week 16. Meandering off in the way it does is bizarre.
FWIW, I'm currently not only discounting the washout and crossover (something UMich have openly stated they've already done), I'm also discounting the control arm of Treatment 1 until I can make sense of that transition. What we have left is still encouraging I believe, even if expectations feel like they're shifting a bit.