Hi everyone, welcome to community! 
Typically this can be resolved, by closing Bitwarden, then in Finder navigating to the location your data is stored and deleting the entire contents of that folder.
Then, relaunch Bitwarden and you should be able to login and sync your data from the Bitwarden cloud as normal. If that doesn’t work and you still need assistance - please feel free to reach out to our Bitwarden Support team for help!