Causes:
1. Abnormal network status
2. Google-related components are not updated to the latest version.
Solution:
1. Go to Google Photos > Photos settings > Back up & sync turn it off and on to try.
2. Clean the Cache on Google Photos.
Path: Long press Google Photos app > App info > Storage usage > Clear data and cache to try.
3. Check Your Backup Status on Google Photos.
If all your photos are transferred to Google Photos successfully, the backup status will show "Backup complete".
If the photos cannot be uploaded to Google Photos from your local devices because the Backup & sync is turned off, you will see "Backup is off".
If your photos are waiting for backup, the backup status will show "Getting ready to back up".
If your phone is not connected to Wi-Fi or cellular data, the status will be "Waiting for connection".
4. Check for the Google Cloud Storage if occupied fully or not.
5. Please update or reinstall your Google Photos to the latest version.
If the above methods do not solve your problem, please back up your data and visit the nearest authorized realme service center for testing.