Dump class name has a STACK value of nnn. When DFSMShsm started a dump task to stack volume dumps to that dump class, the particular set of dump copies (see message ARC0637I for each copy) resulted in spanning to mmm dump volumes (the last one being dmpvol) of the dump class.
DFSMShsm continues.
To reduce the chance of this reoccurring, reduce the STACK value for the dump class before you run automatic dump again.
DFSMShsm