Due to DOS attacks, most keyservers are read-only or have strict upload limits. I can no longer upload my key to SKS keyservers. See also https://gist.github.com/rjhansen/67ab921ffb4084c865b3618d6955275f#executive-summary
The keyservers only have an outdated key of mine, so all gpg –verify checks will fail. For example, in the travis sanity check: https://travis-ci.org/github/bitcoin/bitcoin/builds/664176384
Fix this by switching to keys.openpgp.org as backup.