This error has been happening today on a child form in our ordering system:
The OrdNum field connects to the Title field in the parent. Both exist, and both have non-null contents.
Is this another issue caused by a recent MS update? I rolled back the most recent one after the "Unknown error" problem with New child forms.
Update: This is the console info
spform.js:53 [SharePoint Forms] SPFormSubmissionError: An error has occured while submitting the form to SharePoint.
at new t (https://forms.plumsail.com/widget/1.0.7/spform.js:42:95107)
at e. (https://forms.plumsail.com/widget/1.0.7/spform.js:103:62829)
at Object.next (https://forms.plumsail.com/widget/1.0.7/spform.js:103:55202)
at s (https://forms.plumsail.com/widget/1.0.7/spform.js:103:53943) FormManager:SaveForm