To your below point ALB can not be configured as Static as it will scale up or down dynamically based on demand.
whether App load balancer can be configured static
It would be better if you configure the traffic mirroring session for the Source (if it is a private ALB) and Target instances. Also, take a note of Traffic mirroring limitations, I am not sure that you may be hitting any of these but something to keep in mind.
Lastly, if you are doing this for troubleshooting purposes it would be best to open a support ticket and check the possibilities.
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