An old error message produced by the RA Web is not flushed correctly if a new error message is produced, causing the new error message to not display correctly.
To reproduce wait for a session timeout and try to enroll. You get "Session timed out".
Then try to issue a cert where issuance fails for another reason, e.g. DNS CAA or external process validation failure. You still get a "session timed out" and the new message is not shown at all.