Hi JAta2,
It seems that you have a device in the mail flow that breaks the message structure.
PGP MIME messages work as a single entity, if the structure is modified, the email is broken. This is not the case for PGP Partitioned, as the name hints, the message is composed of different parts.
Did the issue appear only after upgrading? I.e. was this setup working before with a lower version of the SED client?
If you are able to decrypt the .pgp with the PGP Viewer, perhaps something has changed in the infrastructure.
Rgs,
dcats