This is a known issue with UCP. For security reasons, Fandom does not allow minified URLs in page content. The video import tool attempts to copy the YouTube video description as the initial content for the video's file page. Since the video description contains a minified URL, the video tool inserts that as part of the file page content. Then the general page content filter detects it and rejects the content. Failing to create the file page, the video importer rejects the import all together.
The problem Andrewds1021 mentioned has been reported and FANDOM has internally proposed adding back the exception that existed before UCP, but there is no ETA for that. I got this info from FANDOM staff Kirkburn.
You should report it again via "Contact us", since maybe there has been progress since the feedback I got on Oct 8 and you will help increase the priority for them to address this.
This is one of those instances where you can tell FANDOM dev is lacking either expertise of manpower, because they could also just remove or replace the minified URL before it gets scanned, but they don't appear to know how.