It's so frustrating to want to play my games on Stadia and have pixelated everything, glitching and being kicked out of PUBG repeatedly. It doesn't matter if I have 4k off or on, if my Chromecast (playing on my 55" LG) is hardwired directly into my modem or not - I've tried both. Google Stadia speed test shows me bouncing all over. Did it 3 times back to back to back and got 12, 22, 17. All above the 10 Google says you need. Running Stadia on my Google mesh WiFi set up, and Google WiFi app says I'm getting 44mbps to my apartment. Doesn't make a hill of beans difference if I prioritize Stadia in the Google WiFi app. I've made sure both the Google home and Google WiFi app have gaming priority turned on, though I think it's probably one in the same. Oh, and I can shut down Stadia, fire up my PS4 and play COD Warzone without any problems at all. It's maddening. I'm paying $10 a month for Stadia pro because???
It looks like your internet provider doesn't deliver a very consistent connection.
You should try some speedtest.net while using the cable. Check if you are getting the promised speeds thought the day while nobody else is using internet.
The reason you have issues is because Stadia needs a reliable internet connection with low latency.
Sure you can perfectly play your PS online, this way less internet intensive.
My own ISP should deliver 250 Mbps down but during the evening it sometimes drops to 160. Should more than enough to get Stadia running... But it is not only the bandwidth that is dipping... My ping (responds time) raises and Stadia stutters...
My ISP is looking into this... Things like YouTube and Netflix work fine because those services can cache stuff.... This is not possible for Stadia so it needs a decent connection all the time.