Hidden Ability on Corviknight

[Alain]

I can't understand why it gives me error ...
If I change ability, it becomes legit
If I keep the hidden ability (mirror armor) , it becomes "unlegit" (even if then exchanging it gives me no error)

Why?
 

Spoiler

 

[theSLAYER]

Only Max Raid or hatched (and subsequent) Corviknight can have the Hidden Ability.

Since yours is caught at Route 1, it is correct that giving yours its HA will lead it to be marked illegal.