I think there is a differens in the update order.
We Always first update The Delivery Controllers\Director and then the VDA's.
I think the official way is first VDA's and then the Controllers.
Remove the reboot schedule and then recreate it is only working when the controllers are 7.12
(Controllers take the action to reboot an server)
After updated the controllers the reboot schedules where not working. (all versions VDA's)
ater recreating them it works fine.
So i do not know what happens when you first update the VDA's to 7.12 and the controler is still an older version.
I Think recreating the scheduler is not working in that case because the controller take the action to reboot.