This happened when we got our new Samsung phones...it was caused by adding gmail in initial setup of phone, somehow it saw the Google settings from prior phone so we backed up phone, reset to factory settings and setup new phone without adding the Gmail Account until after initial setup was complete...Somehow it was seeing the setting through Google and kept resetting the screen timeout...Tmobile walked us through the problem and advised Gmail was the issue! 😎
Ok everyone. All these solutions may work for you but have yet to work for me. My previous phone with Google setup was set to 10 minutes. My work email is not either the issue as my work doesn't set restrictions and I've deleted of my phone to see if it helps. Auto optimization had been been for a while so that's not the issue. Auto updates would be a solution if it wouldn't happen in the most random nights where there was no updates.
I'm sick of having this issue and I think it's about freekin time Samsung figured out what going on!!
I got a new S10 a week ago and the screen would only stay locked if I did not touch or use the phone for hours, like overnight. Today I figured out that 3 of my 4 "trusted devices" were not connected to my phone, but the 4th, my Garmin Vivosmart on my wrist, was connected. So I switched it to an "untrusted" device, and now the S10 seems to return to the pin lock screen all the time, which is what I prefer. Hope this helps.