jQuery etc not loading after upgrading to Silverstripe 3.7.2

Silverstripe Version:

I’m trying to upgrade to Silverstripe 3.7.2 from 3.2 and a lot of assets are no longer loading.

E.g. jQuery UI:

  1. It does request to this path: index.php/framework/thirdparty/jquery-ui-themes/smoothness/jquery-ui.css?m=1546934157 and gets a 301
  2. it then requests /framework/thirdparty/jquery-ui-themes/smoothness/jquery-ui.css?m=1546934157 and there’s a 500 internal server error.

Any idea why it would behave differently?

Running PHP 7.1, Apache 2.4. My .htaccess has precious little in it:

php_flag safe_mode off
php_flag magic_quotes_gpc off
php_value memory_limit 48M

php_flag display_errors on
php_flag display_startup_errors on
php_value error_reporting 2047