Qatar uses ALTEA. ALTEA has a feature called Theoretical Seating , at T-72 hours it blocks lots of seats for various reasons, trying to allocate groups of seats to allow families to sit together being one, block seats next to status customers, or beside passengers on high cost tickets
check the thread on the BA forum, this talks about some of the BA rules around seat blocking. QR will do similar but may not be exactly the same.
https://www.flyertalk.com/forum/brit...ts-status.html
As more people check in ALTEA will slowly open up blocked seats.