I hate this, because that's probably a fake reason given by them.

Mercado Libre (the "latin american Amazon") did something similar to me: they said I enabled two factor authentication via ID, and blocked me from my account until I give it to them. After a lot of back and forth with support, they finally admitted that they picked random users for "some tests", and told me that there's nothing I could do about it. Maybe LinkedIn is doing something similar?