For some time now, going back to Lightroom 2015.7, when I send a file to Photoshop (always the most recent version) the image opens with Lightroom in background, with no PS workspace — no tool bar, menus, or windows for layers, etc. I am on an iMac with Sierra. When I Tab through applications to PS, then everything appears. I have changed a setting in PS to make this happen?
Please update Lightroom to its latest version 2015.8 and its a known issue therefor you need to open the Photoshop first and then do the edit in from the Lightroom to use the external editor.