I have inserted about 1 million data into a source and executed a SQL query like select count(*) from mv or select * from mv limit 40000, but the query is not returning any result and not reporting any error. It has been in a waiting state for over 30 minutes. There are no error messages in the logs. Query mode seems to have an impact on the situation, where setting it to distribute mode makes it return results sometimes but not consistently, and introduces another error message. What could be causing this issue?