the Utilities manual states about the SYSxxx files for unload/reload:
All SYSxxx files are variable length files. The record length can vary from one step to the next, from one job to the next. Do not code an LRECL value in the JCL, just code a BLKSIZE value. A BLKSIZE value should be chosen based on the optimal size for the device being used, for example, 1/2 track if disk or 32k if tape.
Removing the LRECL resolved this problem.