There is a race between how the curOpMatch was generated and the queryCursor receiving a new batch from getMore. When the cursor receives a new batch, it sets the cursorId to 0 before parsing the response. So it is possible for the test thread to race with the queryThread and get a wrong cursorId 0. Therefore, it is possible for a test to use a wrong curOpMatch {command.getMore: 0} in confirmCurrentOpContents, resulting in test failures.