It 100% sounds like a change from a 3 class to a 2 class. I've had a couple of them in the past few months, and also been in Row 7 which sticks to the booking until you go in and change it. Row 7 just doesn't exist at all on the 2 Class B777s.

Your lucky you noticed it at least a few days in advance and have the opportunity to select other seats.

I would select Row 1 and risk the bassinet not being required. Alternatively, could you split your party in two and choose two smaller groups of seats?