Using SQL Developer 18.4 MacOSX, I'm getting this error
ORA-12801: error signaled in parallel query server P000
ORA-01722: invalid number
When I try to display the tables list in the connections tab.
I've isolated the query (in the log) used by SqlDevelopper.
When I execute each part of the "union all" one by one, there is no error. when I execute the all query I've got the error. When I disable the parallel option, it works fine (ALTER SESSION disable PARALLEL query).