Your documents have the NeedAppearances flag set to true. This makes any signatures therein questionable as it instructs any PDF processor to "construct appearance streams and appearance dictionaries for all widget annotations in the document". Thus, chances are that the signer saw something different when signing than another person viewing the signed document, in particular if a different viewer program is used.
If you set that flag to false (or don't add it at all), Adobe Acrobat recognized the signature.
Your documents have the NeedAppearances flag set to true. This makes any signatures therein questionable as it instructs any PDF processor to "construct appearance streams and appearance dictionaries for all widget annotations in the document". Thus, chances are that the signer saw something different when signing than another person viewing the signed document, in particular if a different viewer program is used.
If you set that flag to false (or don't add it at all), Adobe Acrobat recognized the signature.