Thank you for pointing this out and providing a resolution. This is definitely something to be aware of. Two additional ways I found to find out what the original name was to the repeating section. First, you could go back versions if you are on prem and review what the name was. Second, You can create a workflow that emails, saves to MLT box, or log to history the FormData value in the Item Properties.

I tested a workflow solution by creating a repeating section, added data to a new form, changed the form data control name. And you are right, the data disappears. But while in this state, I created a workflow that updates a MLT field on the item, I use a single action in the workflow, a Set Field action. Configure it to update to the value of fn-XMLEncode(Form Data). Running this workflow on a 'broken' form then provides me an xml value and within it, I find ...><MyRepeatingSection type="System.String">&... which was the name of the repeating section prior to changing the name. Hope this helps if someone has trouble finding the name.

Thank you for this. Curious. What if you did not name it by mistake or just forgot?