Problem:  

Samsung SideSync crashes and displays error messages:

1. Sidesync connection has been lost.
2. USB connection to Samsung Phone has been lost.

Cause:

Sidesync crashes from keyboard and mouse interaction with the remote session (i.e., virtual phone).   This situation occurs when the Keyboard & Mouse sharing are disabled.  N.B., Keyboard & Mouse Sharing is disabled by default.

Solution:

Enable the Keyboard and mouse sharing:

1.   Open SideSync from the notification bar.
   
   
   
2. Click on the "More" button.
   
3. Click on "Enable Keyboard and mouse sharing" menu item.
   
   
   
4. Click on the Phone screen button to initiate screen mirror.

 That's It!