These are the first 7 B787-9 for Qatar Airways. For a type which typically delivers 2-3 weeks after first flight, some have been hanging around at Boeing since a first flight in September, while all the rest of the production for others delivers as normal.
My hunch, adding together the various issues discussed above, is that Qatar have contracted separately, not through Boeing, for the cabin fitout, to be installed in the USA, and that the Boeing contract stipulated airframe delivery point in Qatar. Thus when it was apparent the fitout contractor was not going to be complete by the end of the year they were just flown to Qatar, the airline told "here you are, our bit of the contract complete, sign here", and then flown back. Probably about USD 1 bn then transferred. Boeing need all the cash they can get at present.