i will put myself in the list as well. i already started seeing this issue when using the lightwave plugin when the first octane releases with denoiser appeared. i found then out that the octane.app will have the same issues. my symptoms: mac shuts down hard when using denoiser (with settings to denoise while rendering in progress) in any slightly complex scene scene which uses large resolution. you will need to set it to more or about 2K wide, no matter if final render or IPR. in case the denoising setting is set to 'at completion' it will shut down at that point.
i've heard on PC it's just a shutdown, but on my 2010 mac pro it is a very unusual hard shutdown. you will need to pull the power connection for a few seconds, only then the mac can reboot. i always checked to have enough free VRAM - never out of core was used. also, i verified with a hardware monitor tool that no serious power issues with PSU are the problem. a few months ago i checked this with the lightwave plugin developer juanjo and if i remember correctly he forwarded the question to the core developers.
in the meantime i switched over to C4D and have still the same issue with this platform plugin (and the core app). apparently, small and basic render scenes with small previews / render sizes do not have any problems with the denoiser - maybe one of the reasons why it is not reported by everyone?
in my case it is no RTX card but just an older nvidia 980ti with 6G VRAM. other specs: macpro mid 2010. 48 GB RAM (octanes out of core set to 12G), mac OS 10.13.6, nvidia driver 3126.96.36.199.40.127 and CUDA 418.163 (latest).
my C4D plugin version is V4.0.4-R2.
Apple Mac Pro 5,1 with NVIDIA GeForce GTX 1080 8192 MB, 2 x 2,66 GHz 6-core Intel Xeon/ Mac OS 10.13.6 + networked HP Z600 workstation with 48G RAM, Netstor GPU box, 5 x NVIDIA GTX 980ti / Windows 7 pro.