Cannot login to train wifi

With Fairphone 3, /e/OS 0.17-q I cannot login to wifi on trains (e.g. ICE in Germany), the captive portal login notification does not show up.
It works correct with Samsung Galaxy S5 Plus (SM-G901F), /e/OS 0.17-p.
What may be the reason for this issue? I cannot find differences in settings.

Can you tell if this is because the WiFi provider tries to launch your browser, fails, but requires you to see the T&C page and accept?

I had this once - I got someone to give me the url of the required page, bookmarked it, open it as I login to wifi, accept and go. Sometimes this provider now recognises the device and I logon problem free.

The same day I logged in to another free wifi in a hostel and there the login notification appeared.

If you want to log in to a free wifi and the provider request you to accept the terms, after selecting the wifi APN a notification appears. AFAIK this comes from the system app CaptivePortalLogin. When you tap on the notification the login screen appears.

As said, the notification shows up both in the hostel an trains with my Samsung Galaxy S5 plus, but only in the hostel and not in trains with my Fairphone 3.