This question has been answered by taiyo1578. See the first response.
The first thing to try is manually deleting all files in the core/cache directory and visiting the site with your browser in private or incognito mode.
If you used the UpgradeMODX extra to do the upgrade, you can skip the first step, since it clears the MODX cache files.
If that fixes things, it's either something left over in the MODX cache, or in the browser cache or cookies.
You can also try turning off the compress_js or compress_css System Settings (in the DB, if necessary -- in the modx_system_settings table).
RewriteEngine Off
#RewriteEngine Off