The root cause of the random errors is the incompatibility between the selected routing algorithm and the requirement for session affinity. The weighted random routing algorithm does not support sticky sessions. When both are configured, the load balancer cannot guarantee that subsequent requests from the same user will be sent to the same target instance. This breaks session state for the application, leading to unpredictable behavior and errors.

By changing the routing algorithm to least outstanding requests, the Application Load Balancer can properly implement sticky sessions. This algorithm is compatible with session affinity and will ensure that once a user's session is established with a target, all subsequent requests from that user are routed to the same target, preserving session state and eliminating the errors.

B. Anomaly mitigation is a sub-feature of the least outstanding requests algorithm; it is not a standalone setting and does not address the core routing incompatibility.

C. Disabling cross-zone load balancing alters how traffic is distributed across Availability Zones but does not resolve the conflict between the routing algorithm and sticky sessions.

D. Deregistration delay is relevant for handling in-flight requests when an instance is being deregistered, not for routing errors during normal operation with healthy targets.

1. AWS Documentation: Elastic Load Balancing User Guide - Routing algorithm.

This document explicitly states the compatibility of different routing algorithms with sticky sessions. It notes: "The round robin and least outstanding requests routing algorithms can be used with sticky sessions

while the weighted random routing algorithm cannot." This directly supports the conclusion that the weighted random algorithm is the cause of the issue.

2. AWS Documentation: Elastic Load Balancing User Guide - Sticky sessions for your Application Load Balancer.

This guide explains how sticky sessions work. It states

"Sticky sessions are a mechanism to route requests from the same client to the same target... This is useful for servers that maintain state information in order to provide a continuous experience to clients." This confirms that failing to maintain stickiness would cause the state-related errors described in the question. The choice of a compatible routing algorithm is fundamental to this mechanism.