Etihad frequently manages to f*ck up with the seats. They don't care about reservations, but normally your selected seat should be shown till check in.
On my last 8-10 etihad journeys I always had at least one leg, where no equipment change has happened and still the reservation got somehow deleted at check in, but the seats remained blocked.

Thats one of many reasons that I now booked a flight on QR, after many "warnings" to etihad.