Originally Posted by
WineCountryUA
Yes
give it a week or two and you will need need to reselect the seats.
Seating is not fully enabled for flights when initially released for purchase. But it is just a shortterm issue.
Note that if you were charged for Economy Plus, however, you might have a bit of an issue with that. Most likely case is the website will prompt you for the fee again - pay it and get the original charge refunded.