Taylor Swift attends an event at the Toronto International Film Festival on Sept. 9. Evan Agostini/Invision via AP

Ticketmaster said bot attacks and uninvited fans drove “unprecedented traffic” that caused site outages and long wait times during Tuesday’s Taylor Swift presale, but the ticket seller stopped short of offering the pop star’s fans an apology.

Ticketmaster was criticized for excessive wait times during the sale, and at least one Attorney General is now investigating those complaints, but it said on Thursday that only about 15% of interactions across its site experienced issues.

It said its website experienced 3.5 billion system requests, four times its previous peak, during the presale. About 1.5 million people had been invited to participate in the presale, and 2 million were placed on a wait list.

The uninvited volume “disrupted the predictability and reliability that is the hallmark of our Verified Fan platform,” Ticketmaster said in its statement.

It assured Swifties they will work to improve users’ experiences going forward. A record-breaking 2 million tickets were sold for Swift’s tour, the most sold for any artist in a single day.