Latest Opera updates seem to be going backwards instead of forward. As mentioned before:
There is still the problem with random crashes https://forums.opera.com/topic/33931/frequent-crashing
and there is still not much usable information or reply regarding the state of the current Download Manager and the way it handles files: https://forums.opera.com/topic/33463/suggestion-minor-download-manager-tweaks
Now there is this odd bug, that happens with variety of sizes large files.
Mind you that the ZIP isn't a On-The-Fly ZIP Archive, it's a pre-Zipped Archive stored on a server (AWS S3) and it returns such oddity with the progress bar.