By golly, you were right, @dkg! I ran that "gross hack" (thanks so much for writing it) and after nearly 10 minutes got the output I needed. Last 5 lines:
Jun 28 2019
Jun 27 2019
Good to see you here @dkg, thanks for the response, and whoa, that's quite something!
Jun 26 2019
I've encountered the same problems that the original poster has described; the problems started suddenly on June 24, not prompted by any related updates as far as I can tell. The problems occur with both gpg 2.1.18 installed from the official Debian Stretch package and 2.2.12 installed from stretch-backports.