Just wanted to chime in to say that although randomizing the seed value for the samples is recommended when rendering without denoising, I believe I read somewhere that it is recommended that you do not randomize your seed value if you plan on denoising as it could lead to things like flicker. Are you rendering with a random seed or a constant seed?
I’ll try to find the reference for my comment and report back!
Edit: Until I find definitive documentation, I’ll just post references to any anecdotal evidence that a static seed value is better for denoising: