Shell_menu_triggers disappeared from the Threads list

[ssimop]

There exist cases – I do not know why? – that the shell menu icon disappears when you right-click a file in Windows Explorer. As a matter of fact "shell_menu_triggers" disappears also from the threads list. To reactivate it I have to exit QM and then run it again. I wonder whether there exist :
a) An explanation for this disappearance. Who/what could have disabled this task?
b) A quick way to restore "shell_menu_triggers" without exiting QM.

Thanks in advance.

[ssimop]

Further to my previous above topic I would like to report that I can re-enable shell menu triggers by disabling QM triggers and then re-enabling them (Ctrl+Shift+Alt+D). I wonder whether this is incidental.