If "http2" is set in nginx' config file for the server running the wkd, gpg is unable to retrieve the key: "gpg: error retrieving 'firstname.lastname@example.org' via WKD: General error"
No (failed or successful) accesses are logged on the server during a gpg --locate-key ....
Removing the "http2" from nginx' listen directive ("listen 443 ssl http2 default_server;" -> "listen 443 ssl default_server;") and restarting nginx fixes this issue.
This happened on arch linux with versions:
gpg (GnuPG) 2.2.17