Try handling unclosed sql connections by calling dispose on the engine before it is put back into the pool.

cdplib/db_handlers/SQLHandler.py

@@ -40,7 +40,7 @@ class SQLHandlerPool(metaclass=SingletonThreadsafe):
         if len(self._sql_handlers) < self._size:
             self._sql_handlers.append(sql_handler)
 
-class SQLHandler(metaclass=SingletonThreadsafe):
+class SQLHandler:
     '''
     Resembles methods for executing sql queries
     with different dabase connectors.