Unfortunately libravatar is being shut down on 2018-09-01 https://blog.libravatar.org/posts/Libravatar.org_is_shutting_down_on_2018-09-01/

This is used in the comments plugin to get an avatar url.

It would probably be best to remove the code that tries to use it, in case its dns eventually gets taken over by something that causes some kind of problem. (The shutdown page doesn't say what will happen to the DNS.)

It might also be a good idea to filter out avatar urls in existing comments that point to libravatar.org. --Joey