Try changing read_sql_to_dataframe to take a engine instead of a connection, to see if this will help with unclosed connections to the sql database

cdplib/db_handlers/SQLHandler.py

@@ -501,6 +501,7 @@ class SQLHandler:
         :rtype: DataFrame
         '''
         try:
+            '''
             connection = self._engine.connect()
 
             data = pd.read_sql(sql=query,
@@ -508,6 +509,10 @@ class SQLHandler:
                                **read_sql_kwargs)
 
             connection.close()
+            '''
+            data = pd.read_sql(sql=query,
+                               con=self.engine,
+                               **read_sql_kwargs)
             return data
 
         except Exception as e: