It's working much better now. Things started improving just a few hours after I posted my previous message, around last Friday afternoon PDT. The web page and email channels started giving out vanilla bridges again (usually 2), and I consistently got 2 obfs4 bridges via Moat and the web page. I just checked again and got 3 obfs4 bridges via Moat, 2 vanilla bridges via both the web page and email, and 2 obfs4 bridges via the web page.
I'm not sure how obfs4 bridges being unreachable would have prevented bridgedb from just giving them out anyway (pretty sure it can't tell on its own), or how any obfs4 issues would prevent it from giving out vanillas, but whatever you did starting last Friday seems to have unclogged the pipes. I'm still seeing weird connection issues with the bridges that I do get; sometimes they work, others they fail with similar errors to the logs I reported before, even though I'm just using the stock TBB 8.5.3 release, and connecting it normally without a bridge or selecting one of the built-in default bridges always works fine so there don't seem to be any local system issues. I've no idea what's going on there, but at least bridges are being distributed again. Thanks for your efforts.