The PGP server has the ability to search for PGP Keys on public Keyservers. Once such keyserver that is provided as a public service, free of charge is "keyserver.pgp.com". There are some installations that are not able to reach to the outside internet to query these Keyservers and so having them on the PGP Server will increase the time to lookup keys. As a result, you can delete this keyserver to speed up the internal queries.
Additionally, some ciphers were getting changed back to defaults after upgrade.
Post upgrade of the PGP server, the keyserver.pgp.com entry is reappearing and this needs to be deleted again.
After the upgrade, you can simply delete the keyserver again, but this is going to be fixed in a future release of the PGP server.
For the Ciphers getting added, this has been fixed in 10.5.1 MP1.
If you would like to be informed of this upcoming release, reach out to Symantec Encryption Support to be added to the list and reference this article.