Reported in the Wald forum.
According to a user for him GpgOL regularly freezes the Windows Explorer when S/MIME encrypting.
The only way I see how this is possible is that get_active_hwnd would somehow return the wrong window handle and gpgol would then disable the wrong window when encrypting.
But even then, encrypting should not take so long. Also according to the user encryption works and the mail is sent when outlook is restarted.
The same user also reported that the new async encryption does regularly not close the overlay.