I set my system for Max Performance and Sleep Never. But somewhere along the line, if left alone, it will switch to Power Saver mode and sometimes Sleep 1 minute as well. Doesn't do this while in use internally, but while using Edge, it sometimes drops video for 3-10 seconds. I have two other PC's with other MB's which don't do this, running the same version of Windows (1803 X64 updated to 1/9), so I assume not a Windows problem.

System details: 8700K binned by SL for 5.2GHz, re-lidded, set at X51, 1.35 vcore, AVX -2, BIOS version 1801, 2080ti Strix 011G, 2x8GB 4266 Tridentz set at 4000, Samsung 961 500GB NVMe, U14S cooler, Acer 4K monitor w/hdmi connection. Does the same with an EVGA 1080ti SC2. Operates fine otherwise, passes all benchmarks and 3DMark stress tests. Two TY-143 fans in front, push-pull Noctua 1500 rpm 140mm fans in the U14S. Idle temp about 40 C, power 36 watts.

I suspect the motherboard/BIOS, but can't prove it.