If android boots before gapps has been flashed, a fresh install is required for now. I'm sorry, this is listed in bugs ("You must flash gapps immediately after flashing sfdroid without rebooting if you want gapps or you will run into android issues."), but I don't think I worded it properly. I had the same issue without sfos and just using this cm12.1 and gapps, need to look into a proper fix still. On android, you'd wipe data and reflash gapps, but we can't do that. And regenerating the art cache doesn't fix it either.