Google keeps crawling pages with redirects

Question

My site's permalink structure is that pages do not end with a trailing slash.

Google, however, keeps crawling pages with trailing slash and adds them to 'Page with redirect' in its Coverage Report.

When I inspect any of the URLs, the report card looks like this:

It says that the non-trailing slash page is the referrer, but there is no reference on that page to the trailing slash version. The canonical is also declared correctly, as you can read from the report.

There is also no reference to trailing slash pages in the sitemap.

If I visit any page and add the trailing slash, I can see that it throws a 301 header to the non-trailing slash version, which is what it should do.

Any idea what's happening and why Google keeps crawling those pages? And, most importantly, how I can fix this?