Hmm. Tried again this afternoon, early enough not to be caught in the 25-hour window. I've been seat-shifted, but still can't select a seat.

I was originally allocated 6A, and 6 appeared to be the first row of ET. I tried to move it to 6F last night, without success. At that point, row 6 was looking relatively empty. Today, I've been moved to 7C and row 6 is showing as completely ful. Tried to move one row back but again no joy. Ah well, checkin opens soon so let's see what happens then.