Sounds like it is just slow and not crashed in that case. That changes things a bit.
That would definitely slow things down, especially if extra work is being done per-file (which depends on which columns are visible in the file display, and what shell extensions are installed on the system).
Making a few manually generated process dumps may let us tell you if something outside of Opus is slowing things down: Automatic crash logs (for bug reports)
But with that many files in one folder, it probably makes more sense to split things up and organise them more so everything isn't all in one place, as that will inevitably make a lot of things slow and difficult to manage.