Reusing encrypted message on MITM attack?
You didn't mention the mode of encryption used.
If you are using CBC, predictable IVs maybe an issue.
I would recommend not reusing IV to prevent message replay. You can add a counter inside the encrypted payload and ensure it is increasing.
Notice when you add protection against replay you need to think about out of order etc.
In many cases protocols add timestamps and allow only a limited discrepancy.