Tags with / cause prevPageURL() and nextPageURL() to return invalid links

We have a blog that utilizes tags. One of our tags is: ‘wohnungsmarkt / branche’

If you view the page with that tag (e.g kautionsfrei.de/blog/tag:wohnungsmarkt%20%2F%20branche)

All is good, except the nextPageURL() returns this: https://kautionsfrei.de/blog/%20branche/tag:wohnungsmarkt%20/page:2

If I change the / to an & for example, it works as expected.

I can’t seem to find the source code for nextPageURL() anywhere, so I can’t do any further troubleshooting.