Well, it seems I have found a working solution!!!
This is what I’ve done. As I suspected the cause could be one of the different plugins of the gnome settings daemon, I tried to disable each one of the possible ‘culprits’:
- Screensaver Proxy, as suggested by @joekamprad
I didn’t get the expected result. It seems to be connected with the Gnome screensaver but it didn’t stop the rewriting of the screensaver rules. In order to disable it, what I did was:
If you try to rename or erase the file, Gnome shell simply won’t start.
I thought that this could also be affecting the xset parameters, but it produced no changes, at least, in what we are looking for (the icon themes didn’t work correctly and they defaulted to Adwaita)
This is it!!! If you disable the power plugin and obviously lose all the power saving functions that you can use in Gnome, light locker and any xsettings work out of the box and they remain in the same values all the time. I’ve had it working for a few hours now without problem. The only little thing I’ve detected is that light locker settings sets the ‘turn off screen’ value in the first place instead of the third position, that is:
Light locker settings to turn off screen after four minutes:
Exec=xset s 0 dpms 240 0 0
But it should be:
Exec=xset s 0 dpms 0 0 240
If I remember correctly, gnome power settings could be disabled globally with the dconf editor in the past, but that key seems not to be available anymore.
I hope this can be of any help to you. Please test and share your results!!!