Hey guys!
Yes, this denoising issue is due to the changed (reduced) amount of denoising on bump maps in core 3.
It does less denoising on bumps, in order to maintain more details.
Good intention, but very bad effect on workflow, making quick renders virtually impossible - since the noise on bumps will not be smoothed by the denoiser! Even on value 1 ! ! ! ! ! ! ! ! !
Already asked the developer team to reset this function to the state it was in Core 1.7 - which in my opinion - was perfect!
I hope they will manage to fix it as soon as possible. Because with this issue, test renders in Corona have become a horror !