So,

(The setup)
I have two sets of two PCs that all are running vMix. Each PC in the set has a different role. PC 1 is bringing in two 1080i60 feeds over SDI via a Decklink Duo 2, has 10-15 video elements, some multiviews, an NDI feed with alpha from the second PC which is overlayed on both Decklink Duo inputs via multivew, and is running a light continuous script. PC 1 also outputs via a Decklink Mini Monitor HD. PC 2 has about 50 different GT titles and runs a heavy continuous script. There is a PCI-E network card in PC 1 and PC 2 that is connected directly via a CAT 6, NDI is running through this.

All PCs are Ryzen 7 3800x, RTX 2060 or 3060.

(The issue)
Every few minutes, both video and audio will stutter, some times are worse than others. The weird part is both PC set 1 (set of two PCs outlined above) and PC set 2 (another set of two) stutter at the same time in a similar pattern. It stutters regardless of what is in program, Decklink input, MP4 file, MP4 file via a list.

(Troubleshooting so far)
Each set is on a separate circuit and UPS, still stutter simultaneously. Ran a CPU stress test to see if stutters would get worse, didn't. Updated graphics drivers, no change. Statistics tab shows many dropped frames in NDI input, but if I force NDI to drop by disabling network adapter, no stutter.

Of course ask questions. It would make me very happy to see this resolved!