1. If you actually meant MSE keeps disappearing from SYSTEM TRAY area, then try this.....
Right click at an open spot of taskbar > select Properties > at Notification Area heading, click Customize... > scroll to find MSE > click the pointer at far right and select Show Icon and Notifications.
2. Another suggestion :
Right click at taskbar > select Task Manager > click Processes tab at top > find MSE > click it > bottom right, click End Process > click Applications at top > bottom right, click New Task... > enter the MSE into the Open box > then click OK.
Note : I don't use MSE anymore, so I don't know if it is listed as mse.exe in Task Manager Processes list. When you are at New Task option, make sure you enter exactly the same name as the one you have ended the process.