Once again, this has to be an issue outside of the software, by that you must mean Opus. Because otherwise we would read lots of similar reports here. The usual culprits would be Antivirus, faulty drivers, or hardware problems. On the other hand your report sounds like Opus works normal, once it's running after a fresh start. As long as the reason remains unclear, and no over night task is performed by Opus, maybe a first step would be to terminate Opus before letting your machine run, and see, if you can resume your Opus work without any issues.
There are also a few articles here adressing performance issues, like this one.