OK here is a strange one. On one of my MacBooks, suddenly neither Authy nor 1Password One Time Passwords were working. They would be completely different from my other devices. After spending time with Authy support and not being able to find anything, I saw one strange thing.
The clock on my MacBook was off by about 2 minutes. This was super strange because in System Preferences, I have auto-update clock turned on. Well, I had to manually reset the clock to the proper time and then turn this back on.
Now it all works.
I think what is happening is that being off by a minute or two throws off the synchronization. The entire OTOP protocol depends on the same time across the client and the server. So next time you have this problem check your system clock.