I've been getting this error on one specific release, but not others:

E: 15:48:42,276 webservice._handle_reply:396: Network request error for : Host not found (QT code 3, HTTP code 0)
E: 15:48:42,276 album.error_append:278: Coverart error: Host not found

In Options, I have CAA, Local Files, and CAA Release Group enabled. The weird thing is the "host not found" bit. Seems like that would affect all releases, or none of them. In fact, if I use the Other Versions menu to select a different version, I don't get the error - it's just one specific version of one release:

https://musicbrainz.org/release/d20247ad-940e-486d-948f-be4c17024ab9?tport=8000

If I click on the More Details button in the cover art pane, it crashes Picard entirely.  Log from the log window (prior to crash, obviously) is attached.