Mapframe maps that include images in the GeoJSON code don't display on the mobile website or the Android app or the iOS app. E.g., here is a page that compares a map that includes an image versus one that has no image. (The one with the image doesn't display on any mobile platform; the one without displays properly on the mobile website but not on the apps, an issue detailed in T193313.)
[desktop link] https://en.wikipedia.org/wiki/User:JMatazzoni_(WMF)/maptest
[mobile link] https://en.m.wikipedia.org/wiki/User:JMatazzoni_(WMF)/maptest
for testing purposes, the same maps are on test2, which displays dynamic maps right on the page (instead of static maps, like most Wikipedias), and on ca.wiki, which should be the same as en.wiki but we're just making sure.
[test2] https://test2.wikipedia.org/wiki/User:JMatazzoni_(WMF)/maptest
[ca.wik] https://ca.wikipedia.org/wiki/Usuari:JMatazzoni_(WMF)/maptest
For the mobile website I was able to see that the issue is that the request to maps.wikimedia.org returns a 400 Bad Request.
This is the request done on the desktop website that works fine:
https://maps.wikimedia.org/img/osm-intl,14,-33.92151,18.4213328,400x250.png?lang=en&domain=en.wikipedia.org&title=User%3AJMatazzoni+%28WMF%29%2Fmaptest&groups=_cfd0a90b704aff0ccc1e22cc6f3d7b05a1075ea1
While the mobile website uses a different group ID, while keeping the same domain en.wikipedia.org:
https://maps.wikimedia.org/img/osm-intl,14,-33.92151,18.4213328,400x250.png?lang=en&domain=en.wikipedia.org&title=User%3AJMatazzoni+%28WMF%29%2Fmaptest&groups=_23d973ffe007348f605b87c5808ecf9ed87356f9
That results in a 400 with body:
"GroupId not available"