I need some help please. Not sure if I am in the right section. I have a 2006 XT660R with 79853 km on clock. Yesterday morning the XTR started no problem. I commuted to work no problem. However yesterday when I tried to start the XTR to commute back home, I just heard the starter turning but no movement from the crank or cylinder. I can feel the starter turning but nothing more. The display showed error code 12 with engine warning light on. I then found a nice steep ramp and managed to push start the XTR. I then drove home no problem and found out that code 12 is crank sensor error. I then opened up the generator cover and saw that the gears connecting to the starter are all still 100% intact with no damage but I am able to turn the gears. I then drained oil and removed crank case cover. I saw that gear 3 and the starter one-way assembly turns by hand but the ac magneto does not turn. I then took a 22mm socket and turned the bolt that holds the AC magneto in place and the crank turned no problem. I then started undoing the 3 bolts inside the magneto. I saw the 3 bolts that hold that entire story together had snapped off. I have thus far checked the clearance of the magneto, gears, crank and everything in that area but I see no problems or anything getting stuck.
There is no movement up or down, left or right, backwards or forwards on the crank so seems like the bearings are still good. I drained the oil through a cooking oil filter and found no metal bits. I have not checked the oil filter on the XTR yet but I see no signs of wear on the crank case or any of the gears from the starter to the magneto. I consulted a local Yamaha dealer and they told me they have never seen or heard anything like that before.

So my question is (in no particular order)...
1. What could be the cause for those 3 bolts snapping?

I would appreciate any advice. Thank you.