Galaxy S6 not remembering lock screen wallpaper slideshow sequence

[Jim Morton123]

I use multiple wallpapers for my lock screen & after a while the phone 'forgets' the sequence & will only show whichever one was displayed last when the problem begins occurring. It seems to happen more after I've had my phone connected to the wall charger or the USB connection to my PC.

Any ideas? I'm using Android version 7.0.