The power plan reverting to Power save may be due to Intel's Ready Mode Technology (RMT).
Now there’s no waiting to resume activity on your PC. With Intel Ready Mode Technology, your PC resumes to fully functional in an instant. It works by providing an alternative to traditional sleep—a quiet, low power state similar to the kind used by your cell phone and tablet.
The FAQ says:
Does Intel Ready Mode Technology change my OS power plan?
Intel Ready Mode Technology temporarily changes the power plan to power saver mode when your computer transitions to the Intel® Ready Mode Technology state. On resume, your power plan is restored.
It may be changing your power plan to Power saver but not restoring it on resume. Maybe a bug or a conflict with something else.
Check to see if it's enabled and if so, disable it and reboot. Here's a link to the Setup and Configuration Guide for Windows 7 and 8.1. I didn't see one for Windows 10, but it's probably similar to the one for 8.1.
The above poster Mele20 is currently testing this.