The diagnostics that are being produced were added in version 7.4 at the request of a client that was having a problem with crashing systems. They are turned on automatically when the PDSMCPU-04 message is issued. The actual diagnostic messages are not in the CA PDSMAN Message Reference. However, they are mentioned in the PDSMMCPU-04 message text which says "This message may be followed by one or more diagnostic messages that provide additional detail."
These are diagnostic messages telling us that a PDSMAN STC has lost communication with other systems from a non-normal shutdown. The automated "handshake" function returned and error PDSMDMCP-D5 which tells us that the communication failed. Active PDSMAN systems notice that the crashed system is not around anymore and the first one that notices will issue a PDSMMCPU-04 message.
The best resolution is to make sure all the CA PDSMAN STCs are active and running to maintain communications.