I face the same issue (Berryl AX). Via wwan the captive portal doesn’t show, even it shows I’m properly connected. When I attach a cable to the wan port (found the kpn router in the closet
), then the portal pops up instantly. Tried everything, even entering the captive portal url myself, local dns settings set using the wwan auto provided dns. Rebind attack disabled… whatever I try, not able to make it work.