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.