Hi.
We had similiar problems reported from EU, but after checking with them in details, it turned out that it was not the problem on landing page at all.
EU has really “dumb” system in the background so far and in case there are no clients connecting to network, they will just simply say that banner is not showing up correctly.
Trust me, there are 1000x of deployments around EU and if you do it as Cambium gave instructions, it works.
We had some problems with iPhones, but I think that was also resolved at some point with software upgrade on APs and cnMaestro.
Kind regards