Have you tried wiping the cache partition on your device? Do you experience these symptoms if you test your device in safe mode?
Hello! Follow these steps to put the device into safe mode:
-Press and hold the power button until the 3 options for power off, restart, and emergency mode.
-Once you see these press and hold on the power off option until it turns into a safe mode option.
-Select safe mode and the device will reboot into safe mode.
You can get it out of safe mode at anytime by restarting the phone.
In order to wipe the cache partiotion follow these steps:
-Turn off the device.
-Press and hold the Volume Up key and the Bixby key, then press and hold the Power key.
-When the Android logo displays, release all three keys.
-An 'Installing system update' message will show for 30 - 60 seconds before the Android system recovery menu options appear.
-Press the Volume down key several times to highlight wipe cache partition.
-Press Power key to select.
-Press the Volume down key to highlight yes, them and press the Power key to select.
-When the wipe cache partition is complete, Reboot system now is highlighted.
-Press the Power key to restart the device.
Do you have "Scene optimizer" turned on in settings? I think it might automatically use Night mode when it detects darkness.