For some reason, in Chrome (latest version), Urza Gatherer kept loading as v9.9.7 (or whatever the latest 9.9.X version was).
1) Refreshing the page.
2) Opened dev-tools (with "Disable cache" on), and hard-refreshed the page. This temporarily solved it, but the issue returns as soon as I close the dev-tools and refresh.
3) Cleared all cached images/files in my browser, then redid steps 1-2.
4) Updated Chrome to the latest version, and completely restarted Chrome.
5) Cleared all local-storage and cookies of the site, then redid steps 1-2.
6) Manually went into the dev-tools -> application -> service workers panel, and tried updating the worker; no improvement.
7) Tried enabling the "Bypass for network" option. This worked while dev-tools was open with that option enabled, but the site reverted to 9.9.X when I closed dev-tools and refresh.
8) Tried "Updating" the service-worker, then "Unregistering" it, with "Disable cache" on, then pressed "Empty cache and hard refresh" on the refresh button. Again, worked temporarily, but the site reverted to 9.9.X as soon as I closed dev-tools and refreshed.
Having a background in web-development, I was getting quite annoyed with how the service worker somehow -- apparently -- kept retrieving an old version of the site and trying to run it. I eventually decided there is probably a bug deep somewhere in either Urza Gatherer or Chrome (I suspect it's a bug in Chrome, although maybe there's some developer-side workaround that could be implemented).
In the end, I did finally find a solution:
1) I installed the "Block Service Workers" extension: https://chrome.google.com/webstore/detail/block-service-workers/ceokjgeibfjfcboemhdpkdalankbmnej
2) I did an "Empty cache and hard refresh" of Urza (just to be sure). The extension popped up a message asking if it should allow the service-worker to be installed/used.
3) I said "No"; and yay, v10.0.X showed up as desired.
4) I did some more fiddling around to confirm the issue was actually fixed, including clearing the extension's blocking, trying more hard-refreshes, etc.
5) After that period of fiddling, I did some regular refreshes with the dev-tools closed, and *finally* the issue seems to be resolved. (the v9.0.X has not shown up again since then, thank goodness)
Anyway, since I didn't see any results for this issue during a search for it on these forums, my guess is that the problem is either rare, or something most people don't notice.
It's probably not even worth your time to investigate it. However, because of how annoying/hard-to-fix the issue was, I figured I would mention it on these forums so people in the future can find this information through search, if/when needed.