It could be the screen size. I was using the mobile skin but on a laptop.
As for the customization, it is a bit unclear where that comes from. Based on the list of extensions, it seems like Fandom is now using MobileFrontend but the docs for that say it doesn't load personal CSS/JS. Maybe the docs just mean there is no personal mobile.css? The help page for FandomMobile hints at customization options currently being under evaluation but doesn't give much detail.
Edit: By the way, it looks like our our notification scripts could probably run on mobile with little/no alternations. The problem is it looks like there is no such thing as personal global UCP mobile JS.
Edit 2: I wouldn't take customization on mobile to mean anything for Discussions.