Okay, I cherry-picked upstream commits 487cc27e1..d21a3b622, the endpoint being the current upstream/main, and built, and installed, and it seems to solve this problem. The "no bencoded data to parse" messages are gone. And things verify upon request, with most of them succeeding. A few failed to verify even though they are absolutely downloaded; these are all single file torrents, instead of a directory containing files. So that's a clue as to the bug, I suppose.
Anyway, this issue does seem at least mostly fixed upstream post-release.
