Ok, I submitted 3 bug reports, each time I varied my steps slightly. Hope this helps.

Here's the screenshot I announced in one of those reports.

I'm trying to record video on my D850, but when I press "Start recording video" the app freezes and becomes *extremely* slow after recovering (you can watch UI controls redrawing, that's how bad it is). Recording doesn't work at all. This is with an Xperia Z4 tablet running Android 7.1.1. ...