Process Monitor logs and manual dumps from while the slow-down is happening might reveal something.
Testing with the Opus config reset to default may also be worth a try, in case a script or other config detail is involved. If you want to try that, first create a backup of your config (Settings > Backup & Restore), then uninstall Opus (which wipes the config) and then reinstall it and test things out. After you're finished testing, you can restore the config backup via the same menu item to put things back how they were.