Go in To the OneDrive app and click on the "For You" Tab.
If there is an "Uploading" text link showing, click on that to view the file (s) that are queued. Those which cannot be uploaded to the server from the camera are marked with a red X on the right. Click these to retry the operation, a circular progress arrow spinner should indicate the operation in progress.
If there is no response from either retry or "Uploading", try renaming the existing OneDrive Folder to
Camera RollOld. Stop the backup by navigating to Settings on the OneDrive "Me" Tab, and click "Camera Backup." Then click "TURN OFF BACK UP," after which navigation to "Camera Backup" turns it on again. Then retry the "Uploading" text link to check the sync progress as above.
Once the files are synced, it's safe to rename the folder back to