Are all mobile devices supposed to support custom stencils?

Sorry for the delay. Does this outline works in editor when you switch to mobile preview mode? (MainToolbar - > Settings → Preview Rendering Level → Mobile → Default Mobile)

Also could you attach here log output when you start project on that device? To get filtered log from device you can enable Device Output Log window in editor. (Editor Preferences → Experiemental → Device Output Log) it will appear in MainMenu - > Windows.