problems with signatures

Hi, I've read all posts about this argument but I still couldn't find a solution.

I have a PDF file with signatures.

3 users see the same file with all valid signatures, 30 users with the same adobe version see the same files with not valid signatures.

When I analyze signatures a message tell me that the file has been modified or corrupted since it has been signed.

The funny thing is that when I just open the PDF and make no changes and try to close the file adobe always asks me if I want to save the changes, I always obviously choose no but it asks me that everytime.

On other software that check signatures all signatures are valid.

On a adobe pro version I have no errors.

All computer are windows10 based.

What can I do to solve?

Thank you