I have had the randomest issues with shadow, but I knew they were because of my PC.
Random games causing extreme glitters and artifacts to appear every other second.
My desktop having a lag that made it so if I shook around a window you could get the entire stream to become insanely choppy. But internet was no issue, and at times everything would just work.
I found the answer to this issue,
Sometimes plugging your laptop into serveral different displays changes it's refresh rate.
For instance my Acer laptop can't handle 60hz with any resolution above 2560 x 1440. So whenever I plug it into my TV, it automatically gets set to 30hz. Sometimes when you unplug it the setting will be reset back to original but when it doesn't there will be issues streaming with shadow.
If your shadow is set to stream at 60hz,144hz,30hz, or whatever. And your laptop isn't setup to the same parameters you will get tearing and streaming problems like crazy.
The second I realized this I started double checking my settings after connecting my HDMI to a display. Only after confirming this I make sure the setting in my shadow launcher match before I start streaming and now it's insanely smooth with only 28 ms of latency.
If you got any questions feel free to reach out.