Thanks to my team mates, Cindy and Hector, who alerted me on this newly detected issue. When your database has been upgraded from release to release, it could happen that a public synonym
XMLCONCAT exists. And before you upgrade to Oracle 12.2.01 or Oracle 18c you must drop this public synonym to avoid upgrade errors.
Drop public synonym XMLCONCAT prior to upgrade
The public synonym XMLCONCAT in pre-126.96.36.199 Oracle databases pointed to a PL/SQL function of the same name. In 188.8.131.52, this PL/SQL function was changed to a C function.The public synonym was no longer needed nor pointing to a …Continue reading...