Yup, you won't be able to turn AJAX off, if you have already uploaded cropped data, and your max AJAX files is set to 1. In that case, we store that JSON object you quoted, in the upload element field on the main table, rather than just a file path. Switching AJAX off will yield that error, as non AJAX uploads don't support cropping, and we're then just expecting a simple string for the path, not the crop object.
If you want to turn AJAX off, you'd have to manually empty out the column in something like phpMyAdmin.
I'll take a look, see if I can replicate / fix your original issue, of the upload not showing in form view.
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