This happening on 2 of my desktops as wel, both clean WIn 10 installs. Its hit and miss whether or not it shows up in Windows 10. I have reset system tray icons through regedit as shown below. Malwarebytes still disappears from WIn 10 system tray icon configurations. Isnt even listed in win 10 settings
Back up the Registry by creating a restore point.
Press the Windows key, type regedit, and press Enter to open the Registry Editor.
Navigate to and select HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\TrayNotify.
Delete both IconStreams and PastIconStream in the right pane.
Press Ctrl-Alt-Delete and select Start Task Manager.
Select the Processes tab, choose explorer.exe, and click End Process.
Choose the Applications tab, click New Task, enter explorer.exe in the text box, and press Enter.