First the good news: the 18.1.7 point release contains a nice improvement for EE users: security namespaces are now first-class names in AFL, so you no longer need to provide them as string literals to the various namespace operators.
The bad news is that this change introduced an unanticipated issue with the parsing of arguments to user-defined operators (UDOs). Unless you recompile your plugin, UDOs will fail:
iquery -aq "op_count(my_operator(DATASET))"
UserQueryException in file: src/query/parser/Translator.cpp function: passAFLOperator line: 839
Error id: scidb::SCIDB_SE_SYNTAX::SCIDB_LE_WRONG_OPERATOR_ARGUMENTS_COUNT2
Error description: Query syntax error. Operator 'my_operator' expected more arguments.
In general, Paradigm4 does not support cross-version compatibility between plugins and the SciDB core. Sometimes unrecompiled plugins will work, but as in this case, sometimes they don’t. So it’s a good practice to always recompile your plugins after upgrade.