My master password is not accepted on OSX. I have not changed my master password, I have no Capslock on, I do remember my password, I did retry and it does not work either in 1Password or 1Password Mini. It does however still work on my iPhone.
I did read that other people recently had the same issue, but that no final conclusion was found. I did also restart my computer as mentioned in the post, but that also did not help.
I did also run a diagnostic and send that to the support email.
1Password Version: 6.8.1
Extension Version: Not Provided
OS Version: OSX 10.10.5
Sync Type: iCloud