Timeline Panel missing button in the middle of it, unable to select Create Frame Animation

I've tried reseting my preferences as per https://forums.adobe.com/thread/2317982, but that doesn't fix it.  It does put the button on the panel when an empty document is open, but when I import "Video Frames To Layers" it opens in a new document and the button isn't on the timeline panel in that document.  It's in the other blank document though.  How can I get it to show in the document I'm working in?