Ok, so I’ve tracked it down to a module I’m using:
Not sure yet why exactly the buttons are disappearing, but have submitted a bug report and will keep digging… I have a hunch that it’s not the social-media module itself, but rather one of its dependencies.
Any tips on how to only apply that to selected model admins? Eg. have buttons enabled for SecurityAdmin (prevent the module removing the buttons), but disabled on the ImageEditorAdmin (use the module as intended)?