This is more than an issue of poor quality control, I would call this false advertising. Tiktok below from a friend experiencing issues:
At about 1 minute in, she mentions that TF actually changed the sizing in the website subsequent to the release of the slides. She originally ordered a 6.5 since whole number women's sizing was not originally available. However upon review of the website currently, whole number women's sizing is now visible. On top of that she makes a good point about the differences in Asian vs American sizing which could be the reason for the size discrepancy since TF does source their products from China.
EDIT: To add to the above, I just found out that that while her confirmation email stated she ordered a 6.5, her order summary on the website and delivery information show a size 5 instead, bruh