Example: https://circleci.com/gh/mkobit/gradle-test-kotlin-extensions/26
Comes from the CIRCLE_COMPARE_URL environment variable which is documented here.
The value is https://github.com/mkobit/gradle-test-kotlin-extensions/compare/211a8ef37eb6^...3c546b55628a which has the non-encoded ^. This seems like more of a Circle CI issue with not escaping the URLs, but it would be nice to not have it blow up in the scan plugin. Although, the behavior may be desired from the scan plugin side. so at least documenting on this post will help others that run into it.
Circle CI report: https://discuss.circleci.com/t/circle-compare-url-does-not-url-escape-caret/18464