Thank you for comment.
Regarding print with USB cable: Except MBot Grid II+ other model need to select manually. For example MBot Mini, First Select MBot mini on device select after that connect to device.
On menu, Device => Select type of device => MBot mini after that device => connect to a New Device => COM
Crashing issue: If you post the crashing screenshot of MPrint, It would be helful for us. This is beta version and there maybe some bug which we need to fix as long as we receive the comment from user. It will help us to fix these bug.