With much fanfare, Automattic released a new version of Jetpack Stats for WordPress in March 2023. And sometimes the page doesn’t load, giving the spinny ring of death. Wait all day if you want, you’ll just get the ring. Hitting F5 to reload the page will almost always cause this to happen, as will your computer going to sleep while the page is open. But sometimes I’ve seen it happen on its own as well.
The fix is easy but non-obvious.

Click in your address bar in your web browser, then arrow over to where it says page=stats. Delete everything after the word “stats.” All the rest of the contents of the address bar. Then hit enter to load the page. Now it’ll work.
I’m not sure exactly what the part that looks like #!/stats/day/16321610?page=stats&startDate=2023-03-11 does, but when you get rid of it and make Jetpack calculate it again, it seems to get unconfused. Kind of like a reboot for the stats page.
Since I usually keep this tab open and I’ve been hitting F5 to refresh it for a good 10 years, I was glad to find this fix because I would inadvertently break my Jetpack stats page to make it not load frequently. By frequently, I mean once a day after the new Jetpack upgrade. No exaggerating. So I hope this fix works for you as well as it works for me. Overall I think the new Jetpack Stats is a nice upgrade. I just need to remember this fix when I break it, but since I’ve done that five times since remembering the fix, I think I’m pretty well on my way to committing it to memory.