Pretty much every reboot event should be logged except for physical reboot (Pulling the plug out and in), you can take a look at the example:
As you can see there are a lot of different reboot logs, maybe you can try some of them and see if they are logged? "Request from button" is logged after pressing the reset button on the router for a second (Don't hold it too long because you can reset the router accidentally).
P.S. The screenshot on my last comment did not save, I edited it so you can take a look again.