Originally Posted by
corporate-wage-slave
7K is used as a crew rest seat on longer flights. Usually this is done a few days before departure, or blocked some weeks out, but if there is a spare crew (e.g. from the early disrupted operations) then that may explain this. Hence the advice in this forum to avoid those seats (more of an issue to LAX, SFO, SAN etc).
If this is routine on certain sectors, then it seems silly and clearly frustrating that they aren't blocked from the outset on those routes, to avoid disappointing customers like the OP.