PDSMMCPU-05 MCPU is in SLOWDOWN mode. Messages are issued repeatedly during startup of the PDSMMCPU Cross-System Communication subtask.
This may be followed by various S0C1 or S0C4 abends, causing the PDSMMCPU subtask to fail.
PDSMMCPU is designed to handle this situation by buffering traffic until the slowdown is resolved. However, because this occurred at startup, MCPU was trying to register CPU WSTY in the data set which was already full of the traffic from the other systems.
Instead of waiting until the next MCPU cycle (approximately 14 seconds later), the code continued to try and register WSTY.
This is why multiple PDSMMCPU-05 SLOWDOWN messages all with the same timestamp are being issued.
This continued until PDSM picked up a stray value that could not be formatted into a message, which eventually ended up in a S0C1.
Download and apply PTF ST06477.
This PTF changes PDSMMCPU to attempt CPU registration only once each cycle. If the CPU cannot be registered due to a SLOWDOWN condition, a PDSMMCPU-06 message with a status of "Delayed" is issued and registration is attempted on the next PDSMMCPU cycle until it is successful. A PDSMMCPU-06 message with a status of "Active" is then issued.