Since upgrading to the latest MacOS my Macbook Pro seems to be turning off while in sleep mode if left for a long time, I think only when it's not plugged in.
If I close the lid and open it up in about 10 mins, it'll come out of sleep as expected and ask for my password. However if I close the lid and leave it for a few hours, I need to press the power button to boot it back up again asks for HDD encryption password and then prompts to log in.
I have tried resetting the NVRAM and SMC but no luck. There are no further MacOS updates.
Any idea what else I can try?