we are encountering the exact same issue. Lates 419.67 drivers with 4x GTX1080ti cards. Our system is usually stable (besides the PLX chip issue on our Asus x99-E WS/USB3.1 motherboard). But right now our computer shuts down on every render with denier enabled. It doesn't matter if we enable denier in one or all 4 cards, it just turns the computer off at one point of the render. If we disable denoiser all renders complete no problem. So basically right now the denoiser is not usable for us, which really is a pain, since it saves valuable time. Can someone please see if they have the same issue when they render with denoiser ? BTW, this problem only seems to occur when we render in 1080 resolution. whenever we render in 960 x 540 the render finishes every time. We noticed this by downloading the 2018.1 demo version, which rendered our test with denoiser no problem. But then again, the demo is of course limited to 960 x 540 size, so we gave that a go in 4.02.1 and sure enough it is rendering all through the night without a glitch. Then we just started our render with 1080 resolution and sure enough after 5 minute step computer turns off. It must be a size related problem, we just finished rendering another test in 1280 x 720 resolution and it works no problem. Of course anything over 1080 crashes as well.
If someone can please make a small test with a 1080 animation and denoiser turned on and see if it renders more than 30 frames that would be great. Thanks so much