localStorage not working on iOS captive portal mini browser (CPMB)

I tried to save data on iOS Captive Portal Mini Browser (Hotspot WiFi)
window.localStorage.setItem("my_data", "data");
but when I try to reconnect to CPMB
var my_data = window.localStorage.getItem("my_data");
my_data is null

I have the same problem using Cookies, it works fine on Android, Windows,…

is there any alternative to backup data to iOS device using CPMB ?

Thanks