Currently, the system intelligently schedules L2 IP adress during back-to-origin, rather than recommending a list. The recommended list before may cause back-to-origin failure.
If you have other special scenarios, such as your origin site being installed some security softwares to limit access, use the interface of DescribeL2VipsByDomain.
If your daily average peak bandwidth is over 1 Gbps, you can submit a ticket, so that you can get a L2 IP address. Then, add this address to your whitelist to ensure your service.
Submit a ticket if your problem still exists.