Regarding 301120, I believe this is the expected behavior, since there is no article "Wiki Articles:Specific Title" (the synonym target), just "Specific Title". Maybe this worked in VW3 if the "Wiki Articles:" namespace was the name for the default namespace (""). But this will not work in VW4 unless there is a synonym for "Wiki Articles:Specific Title" => "Specific Title". We could add a step to massively create such redirects during a VW3 import, but I'm not sure the benefit outweighs the data created -- the former format was rare and was always a 301 response in VW3 from what I remember (it is unreasonable to maintain 301 responses indefinitely). Even if we did create the missing redirect, in this case it would be considered a double-redirect, so the redirect would still not work...
For the case of 301121, it looks like this synonym is correctly broken, because it was once a redirect to itself. This could happen if you renamed the target article multiple times, especially if it was renamed back to a previous title.
The Special:ListRedirects page will give you a better sense of whether redirects are turning into synonyms correctly or not. But for the examples listed in the linked threads, I don't see an obvious issue.