DocumentSignature: document modification is detected, but it should not

Dear Adobe Support and Community,

I'm modifying a PDF file to add an AcroForm + signature form fields in a non-incremental document saving way (using a PDF manipulation library), then I append the signatures (form field update to set "/V" + the actual signature) as incremental PDF changes for each.

Depending on how the first step was performed, the signature appending steps result in a document where only the last signature is valid, the previous ones show an error: "Document has been altered or corrupted since it was signed".

Other PDF viewers show no errors, but AFAIK Adobe Acrobat (using on Windows, 64 bit, v2022.001.20169) has it's own kind of document modification detection ways, so probably that strikes in.

I attached an example file, with a self signed certificate. Could you please provide me some details on what makes the signature validations fail?

Thanks in advance,

David