The built-in antivirus is has caused a lot of problems in the past. It may or may not be involved, but shouldn't be discounted.
An example zip/url would be good to save us having to search for a a website hosting a direct link to a large/slow file to download, and in case it depends on the file contents.
Failing that, a process snapshot while in the problem state may let us see which code is blocking on the file, and if it's in Opus itself or somewhere else.