Dashboard Connection Resets on Certain Pages with net::ERR_CONNECTION_RESET

I recently made an existing website into a WordPress multisite, and then added a new site as a subdirectory.

(All of this only occurs in the one subsite.) The first problem was that no scripts would load in the admin. No CSS, no JavaScript. I was told to add define( 'CONCATENATE_SCRIPTS', false ); to my wp_config.php, so I did. This enabled the styling but then caused this:

Certain pages (basically anything but the dashboard) will give me a net::ERR_CONNECTION_RESET error. On Chrome, it freezes. In Firefox, it says “the connection was reset.” In Safari, it gives me a blank page.

When I take the define( 'CONCATENATE_SCRIPTS', false ); out of the wp-config.php, it loads the pages, but I get a more specific error: the same one (net::ERR_CONNECTION_RESET) but specifically from wp-admin/load-styles.php and wp-admin/load-scripts.php. I don’t have a clue as to why this might be.

This problematic subsite has no plugins enabled, and only one theme that has been working perfectly up until this point on another website.

I also called my host and they both reset the server and upgraded my PHP, neither of which helped.

Any ideas?