I think Opus is rejecting the archive because it has some paths that look illegal inside of it. (In some cases we reject such paths in case they are trying to exploit the zip format to cause crashes or worse, although it can also obviously be due to a bug in whatever created the zip as well.)
Both Opus's internal zip code (when the file has a normal .zip extension) and the archives plugin (if you rename it to .zipx) reject the file, and I suspect the reason is the same in both cases.
If you open the zip using 7-Zip, you'll see it has an extra folder in it which is always called the same name as the zip file itself. Rename the zip file and then open it in 7-Zip again, and that extra folder has been renamed again. That suggests the zip file has an entry inside of it which has a null path or which has a path like ".." or similar, which it should not have.