Mobile reflections: editor preview vs play preview

I have a 4.9 scene I’m trying to build for mobile but I can’t get the reflections from sphere captures to work.

They look ok when I set the editor window preview mode to html5/mobile (and i’ve turned screen space reflections off to double-check they don’t contribute) but when I launch from Play->Mobile Preview or build and run it on a mobile device all reflections disappear.

Are there common problems to look for when sphere capture reflections come out black on mobile?