Unrelated to the question but I've also come across issues on the new forms where the user deletes the file but something about it isn't 100% so formulas and other workflow related items still think the file is there and in some cases users are not required to reattach. If you need a short workaround while this bug is sorted out - you could look at a checkbox to 'delete file' that the user can check and have a webhook do an editRecord call to fully delete the file. Thats the only way I've gotten around the glitchiness with the new forms to date.
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Chayce Duncan
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