One document splitting into several once signed

Once in a while when we send a document for signatures to multiple people it splits the document into two once signed.

One version with signer A's signatures and another version with signer B's signatures.

We absolutely need the signatures on one document and I do not know how to merge other than re-sending the entire document (which makes us look highly unprofessional).

This happens once in a blue moon and we do absolutely nothing different when sending these docs - what are we doing wrong or how can we fix this?

-Lo