I've been having mobile data issues with my Pixel 9 Pro XL for 3 days.
Despite a stable and strong 4G signal at all times, my internet performs very poorly (Signal messages take a minute to send, YouTube homepage doesn't load etc). Then suddenly, all the content will be loaded, as if a connection has been made. I have no idea what could be causing it (I have reset network settings)
I put my SIM in my old phone and it seems to work fine.