I have had this issue since I bought the phone but waited to see if it gets fixed in the newer updates (Thought just a software bug) but unfortunately it doesn’t seem like it.
So, let’s say I used the phone then locked it and kept it on the side. It is lying there (Always on display is visible with quick widgets) flat for some time, nothing blocking the sensors (open space/office table/dinning table) or anything of that sort. After a while when I glance at the phone to check if there are any notifications through the always on display, the screen is black! I tap the screen but it doesn’t come on, keep tapping, nothing!? I have to physically press the power button to wake it up.
Hence, I ask the community if they faced a similar issue or is it just normal behaviour?