I discovered a few weeks late, natch, that SKS keyservers are now deprecated thanks to poor security. The weevils finally gnawed through. Public keys themselves still work, apparently uncompromised per se. But an attack using many multiple signatures can crash GPG. For this and many other reasons, it’s best to use the next generation keyserver being built at:
https://keys.openpgp.org
http://zkaan2xfbuxia2wpf7ofnkbz6r5zdbbvxbunvp5g2iebopbfc4iqmbad.onion/
An educated and irate discussion about the insecurity of SKS:
https://gist.github.com/rjhansen/f716c3ff4a7068b50f2d8896e54e4b7e