Summerbreeze

New HP Elitebook 850 G6.

Raising the laptop lid doesn't fix the issue, both screens are black.
Seems to occur (more frequently) since the latest docking station firmware upgrade.
Relevant post: https://community.spiceworks.com/topic/2255741-thunderbolt-dock-230w-g2-outboard-monitor-problems
See also HP Thunderbolt Dock G2 Troubleshoot guide
In particular:

Disable Win 10 "Turn on fast startup (recommended)". Can be done via Control Panel or registry ([HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Power] "HiberbootEnabled"=dword:00000000)
Update HP Thunderbolt Dock G2 firmware -> already done (through assistant).
Update BIOS -> boot in BIOS, select update BIOS. Current BIOS was 1.5.03 (or something), upgraded to 1.6.

... problem seems to be fixed now.
Let's re-enable the fast startup (maybe was still using an old G2 driver).
... Still having some issues. Unplug/Plug the docking seems to fix the issue, but I don't want to do that.
DONE - Keep "HiberbootEnabled"=dword:00000000
DONE - Checked FW again, and in fact the docking FW upgrade did fail. Try to reinstall... installed manually, now the installer reports that all components are up-to-date.
DONE - Say that Fast Boot must be disabled in BIOS for pre-boot usage. Not sure if this is necessary, or what are the consequences...
... No more issues reported after several days... Issue is back after ~5 days.
DONE - Using a HP monitor with DP native connection -> Still have the issue (immediately)
DONE - Configure HP monitor. Disable DP low-power (set to always active). Disable auto-source. Set DP as default source.
DONE - Still problem. Note we hear some sounds from windows (like device dis-/connecting) after some time of inactivity.
DONE - Power option - when plugged in, don't turn off the screen anymore (currently, both sleep and screen off is disabled).
... let's see ...
More possible alternative fixes:

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