If no user or group information is reaching Firefly, it's likely a problem with the Cloud Uploader.
The first thing to check would be the checkbatches screen. You can access this at:
Look for batch number 1 which is responsible for uploading the actual users and groups, as well as batch number 2 which is responsible for uploading the relationships between those users and groups.
If those batches aren't there, your Cloud Uploader isn't running correctly and you should check your scheduled task that runs the Cloud Uploader. This will likely be on your MIS server and will be labeled Firefly Cloud Uploader or similar. Select the task, then choose the History tab to see how the task has been running recently. This will often shed some light on the problem.
If batches 1 and 2 are present and have been uploaded recently, then your Cloud Uploader is successfully running and you can leave the scheduled task. However, the data that is being uploaded is obviously incorrect and should be rechecked.