Looking up update.FreeBSD.org mirrors... 3 mirrors found.
Fetching metadata signature for 11.4-RELEASE from update4.freebsd.org... done.
Files on mirror (11.4-RELEASE-p4) appear older than what
we are currently running (11.4-RELEASE-p5)!
Cowardly refusing to proceed any further.
Whoops. Mirror ran out of disk space and couldn't extract the latest bits. I'm freeing up some space.
Mirror is updating, should be back in sync within an hour.
Looks like everything is good now. Thanks for reporting.