Problem/Motivation
When using the Views UI to rewrite a field as a link and using a protocol-relative URL (the ones that start with "//"), it is considered as an internal URL and prefixed by "internal:/". This triggers the Core PathValidator that calls the PathProcessorManager::processInbound which can cause a lot of problems. In my case, file URL served by the CDN module become unusable due to their transformation that's not supposed to happen on display.
Proposed resolution
Use \Drupal\Component\Utility\UrlHelper::isExternal() to prevent this from happening.