Answer:-1. Nothing, there are no single points of failure in this architecture.
Note:-
You need multiple ELB if you want HA across regions.
ג€AWS Load Balancer ג€"Cross Network
Many times it happens that after setting up your ELB, you experience significant drops in your performance. The best way to handle this situation is to start with identifying whether your ELB is single AZ or multiple AZ, as single AZ ELB is also considered as one of the Single Points of Failures on AWS Cloud. Once you identify your ELB, it is necessary to make sure ELB loads are kept cross regions.ג€
Reference:-
https://www.botmetric.com/blog/eliminating-single-points-of-failures-on-aws-cloud/