As always, thanks for the very thorough write up. My immediate thoughts were highlighted in the "Discussion" section. Namely, the demographic of your website might respond more negatively to the presence of ads than the general population. This seems to be substantiated by the unusually high use of ad blockers (~60% vs ~18% [1]).

I also wonder if some of the drop off could be explained by the use of Patreon and ads. For instance, I would never pay for Hulu because they still show ads. Did you receive any Patreon cancellations or negative feedback from pledged users?

[1] US ad block usage as of Feb 2017 https://pagefair.com/blog/2017/adblockreport/