Are any crash dumps created, matching the date/time of the crashes?
Have you tried reinstalling Opus over the top of itself, in case something's wrong there?
If so, an extra step is to try a fresh install with completely default configuration. Do a config backup first (Settings -> Backup & Restore), then uninstall Opus (this will wipe your config, which is what the backup is for), then reboot and reinstall Opus. (Don't restore your config backup yet. Use Opus for a while to see if the crash still happens. If it doesn't, there may be something in your config which is triggering the crash.)
Other general suggestions can be found here: General slowdown or instability investigation steps