Thank you AerocatS2A.
Based on my operation, there is no ACARS messages stored locally in the MCDU. So, would you mind if I ask you which is your ATSU P/N or version? I think the version of ATSU has the effect on this issue.
Currently, I have been checking the AOC application and ATSU SW. These two software need to have the compatibility index matching in order to be able to decode message via ATSU.