CSS being copied to other pages

I have a CSS file set up for a specific page, however when I click on some other pages(but not all) the CSS rules are copied over. I don't have any particularly relevant code to show, as it's a pretty basic setup of CSS being specified for certain routes.

Any ideas on how this could be fixed or what could be causing this?

The issue mentions page-specific CSS and route navigation but names no files, tests, or reproducible example. Start by reproducing navigation between the affected routes and inspect when each page's stylesheet is loaded; done means styles from one route no longer appear on unrelated pages.

Written by the indexing model from the issue text.