If your render farm is made up of both Windows and Mac OS workers, you may see inconsistencies from frame to frame, depending on the worker's OS.
What is happening?
When building a render farm, there is a general rule of thumb to "never mix kernels". What is a "kernel" you may ask? The Kernel is the central code to an operating system.
The way Windows PCs and Macs handle random number generation is different at a kernel level. Things like noise, procedural textures, or anything that uses a random seed parameter are the most affected by this.