The concert originally featurs Pekka Kuusisto. Late March he can’t make it. Assistant Concertmaster Yuan-Qing Yu stepped up, learnt the concerto in two months and performed it for the May 21 week concert. You can read more about the interesting story here from CSO.

Fun fact: Kreisler wrote the concerto in 1927. For eight years or so, he claimed it had been written by Vivaldi.
Read more about the performance here from Chicago Classical Review.