A while ago when the seat block was apparently working it actually required a bit of going around. I was on a same E190 flight in Y with a friend (AY Silver) and both of us had our own separate bookings. The seat next to me was showing as free in my screen but shown as taken on his. When I changed to a different row the same happened. In the end he had to select his seat first on a free row and then I selected the free seat next to him