I was able to try Stadia on a Pixel 2 XL, on a Chromecast Ultra, on a desktop PC with a wired connection and on my Chromebook. Stadia worked great on all those devices, except on my Chromebook. The performance was nearly unplayable, because of the high latency and the mouse stuttering. I had a solid 5 GHz WiFi connection, with a high bandwidth (250MBit/s) and the latency was arround 11ms on a speedtesting site. I heard that the performance varies from Chromebook to Chromebook, so i was curious if you have similar experiences with the HP Chromebook 14 G5 (in my case the 3GJ73EA) or with other Chromebooks?
Is it possible for you to view the CPU usage while using Stadia on your Chromebook? You can use an app like Cog (https://chrome.google.com/webstore/detail/cog-system-info-viewer/difcjdggkffcfgcfconafogflmmaadco?hl...) to see this information.
That model of Chromebook has a *very* modest CPU in it. If there is something going on overworking the CPU, it could cause the kinds of behaviors you mentioned.