Computer: Thinkpad T460p GPU: NVIDIA GeForce 940MX Integrated Video: Intel HD Graphics 530 OS: Windows 10, 1709 (Fall Creator Update) Cable: Full size Display Port
When Windows tries to put the displays to sleep after X minutes, the P2415Q will show "Entering Power Save Mode", go to sleep, then turn back on in ~30 seconds, at which point it repeats the loop again.
This happens both with the laptop docked (using full size DP to DP) and un-docked (using laptop mDP to P2415Q full size DP).
It does not seem to happen when hooked up to a MacBook Pro 15" Retina (~2015), using TB to DP.
I have reinstalled Windows 10 without any Lenovo drivers, and the same behavior occurs.
Seems like the same issue could be happening here, with a Surface Pro 4.