XPRAS_SHD_AIMMERGE vs XPRAS_AIMMRG

Good day,

I would like to know on the difference between both of the phases above, one being executed during the pre-processing on the shadow instance, and another being executed during the execution roadmap.

I'm curious as one of the XPRA execution succeeded during the XPRAS_AIMMRG (actual execution), but returns RC=8 during the XPRAS_SHD_AIMMERGE (pre-processing).

Appreciate if someone could help to explain.

Thanks,
Henry