I have experienced a few occasions where the one time codes being generated by 1Password for Mac have been incorrect. I verified that the secret, which is stored as an otpauth:// URI, is correct. I was able to use the secret in it to successfully setup google authenticator to generate valid codes. I was also getting valid codes from 1Password on my iPhone. This indicates that it may have been a problem with the clock, but my Mac's clock was always showing the correct time.
However, the problem is not persistent. Even though it was generating invalid codes for several minutes, as I was comparing with the apps on my phone, at some point it started generating valid codes again.
This is the second time I have noticed this issue within a week for 2 different sites.
1Password Version: 6.8.3
Extension Version: Not Provided
OS Version: macOS 10.13
Sync Type: Dropbox