In mongodb/mongo-php-driver#516, a user encountered the following error when iterating on a large result set on a find operation that included a "local" read concern level:

Failed to parse: { getMore: 44504619209605, collection: "customers", readConcern: { level: "local" } }. Unrecognized field 'readConcern'.

If we look at _mongoc_cursor_cursorid_get_more(), it calls _mongoc_cursor_prepare_getmore_command() to create the getMore command document. That document is then passed along to _mongoc_cursor_cursorid_refresh_from_command() and executed with _mongoc_cursor_run_command(), wherein a readConcern field may be appended. The logic for appending the readConcern needs to be a bit more restrictive so that it only triggers for supported commands.