Strangely, on only one sequence of a project render animation, we have a lot of noise jittering : from good to bad to really bad frames. Half rendered images are just unusable :
look one frame before and the other one just after, result are drastically different. We don't use any denoiser here.
Two things jump to mind - what happens if you render with the variance oracle disabled? - are you able to replicate the issue with a simplified scene? (and therefore can submit a bug)