If you want to use the Oracle XE database in your development/test environments with BPM 18.104.22.168, you will need to make sure to follow the advice on the download page:
If you want to use XE you can set the RCU_JDBC_TRIM_BLOCKS environment variable to TRUE *prior* to running RCU. As a reminder as to support level, when running RCU against XE you will receive a warning stating that the database version is not supported by Oracle.
If you do not follow this advice, you will get a few invalid objects in the database. Remember that XE will work fine for development environments, but it is not actually a supported database for the BPM repository. In production, you should use one of the supported databases.