If you are syncing someone with a lot of ADFS groups, the server may reject the request for the header being too large. If you are able to login as a user with a few groups in ADFS but run into an error with users with a lot of ADFS groups (regardless of if those ADFS groups are in Cinchy), you will need to make 2 changes.
In your CinchySSO app settings, you will also need to increase the max size of the request header.
For more details on the app settings see the app settings section of Configuring ADFS.