When the frontend tries to load de.serlo-staging.dev/_next/static/Xi-6lAt8rBvyzVsDMDnU5/_ssgManifest.js, it gets redirected to https://de.serlo-staging.dev/mathe/5/mathe.
Fixed and deployed now (modulo caching). @kulla: feel free to create an issue for the second part that we discussed earlier if you want to approach that.
When the frontend tries to load de.serlo-staging.dev/_next/static/Xi-6lAt8rBvyzVsDMDnU5/_ssgManifest.js, it gets redirected to https://de.serlo-staging.dev/mathe/5/mathe.
Related to https://github.com/serlo/serlo.org/pull/540