Different Acrobat and Foxit Reader validatation of signatures results ?

Hi everyone. I has just a pdf file that output 2 differents results of signatures validations. One is All signatures are valid as Document is not modified on Foxit Reader, other is 3/4 signatures are invalid as Document is modified on Acrobat.

I assume to sign the document only on signature field and no modification on content on whole sign process. Here is the link to the online European Commission validator for double check, and the result is same as one from Foxit Reader, no signature is invalid (of course those certificates cannot be found or checked, document is not modified at all).

Please check my question and reply if you need any further information.