I have a similar problem. After a while (few cycles of sleep, wake up, hibernate, etc), the screen brightness cannot be adjusted anymore and is stuck in its previous setting. Changing the settings in Windows has no effect. The only way to make it reactive
again is rebooting.
After the problem occurred again, I installed the graphics drivers provided by the supplier (Dell XPS 13 9370). After installation, the brightness settings respond again. This is probably similar to rebooting. However, I will see whether this solved the
problem. I unfortunately forgot the check whether the driver version I installed is older than the previous one.