Hope you are doing well and sorry for the trouble. As described, you are unable to see the subscriber certificate used to sign the document
Would you mind sharing the workflow/steps you are doing to check the subscriber certificate?
Are you trying to validate the digital signature? If yes, to verify the signer and the signed content. Depending on how you have configured your application, validation may occur automatically. Signature validity is determined by checking the authenticity of the signature’s digital ID certificate status and document integrity.