I experienced this problem once, but following these instructions: updating the form version in InfoPath Designer, publishing the changes, and then downloading, deleting from SharePoint, uploading, and re-linking each form did not fix the issue for me. I still experienced the error when attempting to open each form in the browser.
I was able to fix my broken forms by opening each one in InfoPath Form Filler and then submitting them back to SharePoint. After this I was able to edit each form in the browser without any errors.
I opened each one in filler by clicking on the ellipsis menu next to the form's name and selected "Edit".
I still can't figure out the root cause of the issue with my form, for some reason any schema change causes this issue. I have never had this problem it on any other form I have designed using InfoPath. Schema changes can cause data loss, but usually not "Schema Validation Found Non-Data Type Errors".
I may have to re-create the form from scratch.