It should be visible.
I think it is only invisible for me.
You seem to think that invisible signatures are somehow bad. They are not. At least not in general.
But if you are sure the signature should be visible in the document, and if the document is not confidential, you may share it here, so we can analyze it. If the signer cooperates, you may alternatively create a new document without confidential information, let the signer sign it, and if the signature again is invisible in contrast to expectations, you can share that document.