Hi @jegankarthick, I wonder if you have any advanced with the issue on captive portals. From this side we have a consistent delay of 45 seconds since the iphone try to reach the domain of the page, until it is push by the Apple Push Notification Service on the iphone.
I suspect that is because my portal is only in http, in the capture of wired shark I can see that there is communication between the Iphone and some Apple IP's (17.57.144.27) with TLSv1.3 format. Maybe the Iphone try to reach the domain in https with SSL certificate, because it does not exist after the 42 seconds opens the http format by the APN service.