Dear Roger Rose UTofA,
Thank you for reaching out to the Microsoft community. We are delighted to offer our assistance.
I understand that you are experiencing issues with missing data on a synced Forms spreadsheet. When you sync a Forms spreadsheet to a new spreadsheet, it creates a new copy of the original spreadsheet with the latest data from the form. It is possible that the missing data was not included in the latest sync.
To link the form back to the original spreadsheet, you can go to the Responses tab in Forms and click on the three dots next to the response spreadsheet. From there, you can select "Unlink" to unlink the current spreadsheet and then select "Link" to link it back to the original spreadsheet on SharePoint.
Suppose you have manually updated the spreadsheet and want those updates to be reflected back to the SharePoint-based spreadsheet. In that case, you can try manually copying and pasting the data from the updated spreadsheet to the SharePoint-based spreadsheet. If the issue persists on your side, we are afraid that in order to address this issue, it may be necessary to investigate the environment on your end. As forum support, we do not have sufficient permissions and resources to perform an investigation directly.
We have noted that you have posted this question in the For Business category and assume that you have a Microsoft 365 for Business subscription. Therefore, we sincerely recommend that you contact your Microsoft 365 administrator and follow the steps outlined in this article to create a support ticket and contact Online Support.
The support team at Online Support has higher permissions than us and can remotely examine the situation on your end, gather more resources, and assist you with troubleshooting. This will be a more efficient way to address your concerns.
Thank you for your understanding and cooperation! Have a great day.
Sincerely,
Sean | Microsoft Community Moderator