In case the system responding slowly, while it seems the application server itself is not using high resources, then usually the symptoms appearing because of slow or timeouted SQL operations.

It can have multiple reasons:

- Network issue (in case the SQL server is on remote server)
- Limitations of SQL Express 
- Insufficient resources of SQL server or configuration limits  (Number of connections, memory usage)
- Hardware failure (e.g. hard drive)
- Connection parameters needs to be optimized

For this last one check the "poolsize" parameter in ...\Program files\Q-net\Pro 6\conf\database-pool.xml. 
If it is 4 or less, it might help if increase the value a little bit. (e.g. in case of 4 as current value, set it to 6).
This will allow for the application to use more connection to the database.
Too high value is also not recommended as it is causing "deadlock" or "lock request timeout" events and the result is again slow or unsuccessful SQL operation.