Sleep without waking (problem with external monitor)

I have an XPS 15 9550 laptop with the 4k touch screen, with a second 4k Dell P2415Q monitor connected via HDMI.
It's running Windows 10 Pro version 1803, and the desktop is extended across both screens. I have both screens set to 3840x2160, at 200% scaling. Drivers are all up to date.

There are several irritations when the laptop wakes from sleep.

Firstly, the external monitor does not come to life when the laptop does. I have to use the monitor maintenance buttons to wake the monitor.

Secondly, any windows open on the external monitor when the laptop went to sleep are repositioned on the primary monitor when it wakes. I have to reposition all the windows again.

Thirdly, despite both monitors being set to use the same resolution and scale, at some point in the sleep/wake cycle either or both of these parameters has been changed, because (once I've moved the secondary's windows back) I can see that the primary monitor's windows have  typically been redrawn in a new location and then resized, and all the desktop icons (which are always just on the primary screen) have been rearranged as though the screen real estate was transiently significantly smaller than its 2840x2160px.

I'm not sure whether these are bugs or features, but in combination they are extremely annoying. There is of course an easy workaround: disable sleep entirely, but I'd rather have whatever is wrong fixed if I can.

Cheers
T