wondering how this happened? any way to guard against it?
Possibly the config file was corrupted.
We've seen it happen with anti-malware/anti-ransomware tools which decide a name within one of the paths in the XML is sensitive data and then block Opus from reading or writing that data or the whole file.
Using Settings > Backup & Restore occasionally to create a backup of your config is always a good idea.
Sure I believe in backing up. No way to do it automatically within dopus I presume?
If it was caused by protection programs, and I do run both Malwarebytes and win defender... Can I set a directory or file to be excluded from scan?
Thanks
For Defender, instructions are here: Problems caused by Windows Defender (strange behavior when using Opus)
For Malwarebytes, I'm not familiar with how it is configured. Their documentation/support should tell you.