The good news is that Lemmy is now surrounding your spoilers with the expected Details and Summary tags, and moving the HR means PieFed is able to interpret the Markdown for both spoilers.
The bad news:
It turns out KBIN doesn’t understand Details/Summary tags (even though a browser on it own does, so that’s KBIN’s problem).
Neither PieFed, or KBIN, or MS Edge looking at raw HTML can properly deal with a list that starts at ‘0’.
Lemmy is no longer putting List tags around anything inside the spoilers. (so this post now looks worse on KBIN. Sorry about that KBIN users)