Screen Saver mode does not work properly

[Staincross]

When I activate Screen Saver mode in display settings and start it with "Start now" or waiting for the time out, the screen saver shows for a split second before the screen goes completely black, with the exception of the soft keys showing at the bottom.

There is no Night Mode active.

I have tried a couple of different screen savers with the same result.

I am running Nougat.

Has anyone else experienced this or confirm the behaviour?  Is there a fix?

Thanks in advance

[tiffanywatson]

my results on XZ are basically the same. 6-7.5 hours of SSM during two days with moderate use, and 5-ish hours of SOT during 3 days with light use, with 10-15% left by the end. Brightness is also about the same level, but constant WiFi or 4G data transfer plus crappy 4G network at home.

[Staincross]

I've had a system update since posting this.  The problem still presents itself.  I have tried a couple of screen savers, Colours and YoWindow.