Custom module interfering with CSS on /user page

Question

I am having trouble with a custom module. When my site is working properly, the /user page loads 4 CSS files. After rebuilding the cache, only three files load. It's not a 404, Drupal doesn't even try to load the last file.

If I disable the module and load the /user page, the CSS loads properly. I can then re-enable the module and the /user page continues to work. Doing a cache rebuild breaks it again. I'm wondering how that CSS file is generated, and how I can make it load properly when my module is enabled.

Oddly, this issue occurs even if I remove all implementation details from the module: the xyz.services.yml file and the src folder. The only remaining files are README.md and the barebones xyz.info.yml file:

name: XYZ Customizations
description: XYZ-specific additions and modifications.
package: Custom
type: module
version: 1.0
core: 8.x

I'm very confused why this might be happening. Any insight would be appreciated. Thanks!

Answer 1

As it turns out, my custom module folder had the same name as my site's active theme. I believe this was causing the error. Renaming the module appears to have resolved the issue.