I have a similar issue with my Thinkpad X1 Yoga 3rd Gen tablet, connected to a Thinkpad Thunderbolt 3 dock.
When I leave it, sometimes it will go to 'sleep' (I think) - the screen is blank and it will not respond to any mouse or keyboard input, or a short press of the power button.
Initially, I had to hold down the power button to power to turn it fully off and then press the power button again to power it back up.
However, now I have found out that it will come out of this sleep mode if I disconnect the thunderbolt 3 cable! However, the thunderbolt 3 is used for both power and data, so I lose network connectivity (but it might have lost network connectivity anyways when it went in to this sleep mode).
I had previously tried chanting the registry setting to enable the 'unattended sleep timeout' setting and set it to 0 to disable it:
https://appuals.com/windows-10-sleeps-a ... nactivity/
However, this did not seem to prevent it from going in to this sleep mode.
I then used the Lenovo System Update to make sure all my drivers were up to date, including the BIOS, which was a few revisions behind. I've updated the BIOS to 1.30 (21/02/2019). However, even after all these updates, the issue still occurs.
This is an issue for me because I need to leave this laptop on and for it to be active all the time, so that I can get remote access to it (for work) so if it goes in to sleep mode I am not able to remote access to it.
Any other tips to try to resolve this issue? I haven't tried leaving it undocked, but since I have all my screens and connectivity through this dock for normal use, it is a bit impractical, but it may just rule out/in the docking station.