agdm619 We've checked into this and I can confirm regarding the bug you described. Apparently, if you edit an entry that contain signature data from older versions, it will delete the signature for that particular entry. Which is incorrect.
Due to different backend data format, the new signature field won't be able to UPDATE an existing signature, but it will allow you to REPLACE the old signature.
So, the expected behaviour when you have an existing signature field is that the new signature will display an empty signature canvas when you edit an entry and still keep the old signature when you save it (unless you deliberately update the signature itself of course).
We've updated MachForm v12 package with this bugfix. Please login again to our site and re-download machform package. For this particular bugfix, you'll only need to update one file: machform/includes/view-functions.php