PSA beware of stihl electric tools. Their motors are half baked.
The housing rusts and then the magnets flying off and gets crushed to bits. This motor was from their first generation electric mower that was stored in a shed and only used by a homeowner when it wasn't raining. Their chainsaw uses the same motor and has the same problem from my research.
I already attempted cleaning off the rust in the second photo. That spot with no magnets was covered in rust.
As for the failure mode, I suspect that the passivation was flawed. Allowing the evening dew to form rusts that would dislodge the blue plastic bonding the magnets to the housing. However if this was true, it boggles the mind that this problem was never addressed. or was it silently addressed? Regardless, people with this problem are left to macgyvering their own solution because Stihl doesn't care.