I'm not sure whether it is important to you to continue investigating this situation.
If you do want to look into it further, it may be interesting to see what changed about the qtrees in question on Thursday, from OCI's point of view.
select * from dwh_capacity.qtree_dimension where tk in (15259, 15260, 11266, 11267) order by name, tk;
It would also be interesting, for a qtree where you can reproduce this problem, to compare what you see in OCI with the output of a listing of qtree sizes from the ONTAP command line, such as "quota report".