Some phones are among those we have experienced that have unique operating systems in how they handle redirection on captive portals since it is different than almost every other Samsung and Apple phone on the market.
To provide the network to mobile devices, their operating system closes the CNA window (Captive Network Assistant) window right when it finds internet, which is the main issue. Currently, it is difficult for our system to distinguish them because of how many updates and changes they have had over the last year.
At the moment, our system cannot force it to stay open or trick it, without causing connectivity issues. Rest assured that we are working on ways to make splash pages more dynamic so that redirection isn't as big of an issue.