[slampadang]

Ok, the Note 8 is an old phone, but it mostly still works for me. BUT...
I like to have my Display / Screen timeout setting at 5 minutes. Very annoying when you set your phone down for a sec and it's locked. 5 minutes works for me. BUT after a recent factory reset this setting is constantly resetting itself to the default of 30 seconds. This unwanted and uninitiated change happens overnight, or sometimes within the day. Thanks!

[B. Diddy]

Is a power-saving mode turning on at some point? If so, that might be changing the screen timeout.

[slampadang]

Power mode is set to Optimised, which is the same as it has been for years. That was my first thought. You can customise some of the power modes by selecting a different one. If I change power mode, and then re-select Optimised, the settings are not customisable.
I will try now setting to High performance to see it that works. Problem with that is my battery is not too crash hot, unsurprising as it it nearly 5 years old lol