When using the AWS Application Load Balancer as a load balancer for the failover configuration of FlexiCapture 12, the connection from the Processing Server to the Application Server (through the AWS ALB) can not be established.
The returned by IIS code 401 1 2148074248 is related to the sticky sessions settings:
SEC_E_INVALID_TOKEN: The token supplied to the function is invalid
AWS ALB is using cookies to control affinity. It can not be used to balance load coming from FlexiCapture thick clients like Project Setup Station, Verification Station and Processing Stations.
In case you want to balance load from FlexiCapture web clients only (Web Verification Station, Web Capture Station, etc.) you can use AWS ALB with ALB cookies-based sticky sessions.
In case you want to balance load coming from FC thick clients like Project Setup Station, Verification Station and Processing Stations, you cannot use ALB and need to use Network Load Balancer that uses IP addresses to control affinity.