Client Certificate does not working on safari private mode after upgrade IOS to 13.4 (after 26/03/2020)

I have a site which using CA (Certificate Authority) to let user access. After update IOS to version 13.4 (26/02/2020), it's does not working on Safari's private mode. (Works as expected on Normal mode or using Chrome.) The certificates still displayed after load the page but end user cant choose it. After a few times it response Safari cannot open the page because the network connection was lost


Condition:
Operating system: IOS ver 13.4 (after 26/03/2020)

Browser: Safari

Mode: Private mode


Does anyone have idea for this issue? Thanks