Optimizing cPanel deployments for scalable infrastructure hosting?

We're running 'Website Maintenance & cPanel Management Services' for a growing client base and need to streamline cPanel account provisioning and updates across multiple dedicated servers. Our current automation process is becoming a significant bottleneck, impacting our ability to maintain promised SLAs for client sites.

We're encountering a persistent issue with idempotent cPanel API calls for package and account modifications. Specifically, when attempting to programmatically adjust resource limits (e.g., using pkgacct for backups or modifyacct for resource changes) via WHM API 1, we're seeing intermittent CPanel::Exception::API::NonExistent errors or timeouts. This occurs even when the account demonstrably exists and the server is not under heavy load. The problem is most prevalent when executing a rapid sequence of operations on different accounts, or multiple operations on a single account across various hosts.

We've tried a few things to mitigate this:

• Implemented exponential backoff and retry logic for all API calls.
• Switched from JSON-API to XML-API to rule out parsing or formatting issues.
• Thoroughly verified network latency and server resource availability (IOPS, CPU, RAM) during reported failure windows.
• Explored using cPanel UAPI for certain user-level operations, but WHM API remains essential for account management at our scale.
• Considered direct database manipulation of cPanel accounts (MySQL), but deemed it too risky for production environments due to potential data corruption and lack of official support.

The issue typically manifests as either a 500 Internal Server Error from the WHM API endpoint or a specific CPanel::Exception::API::NonExistent message, despite the target account existing. For instance:

{
    "metadata": {
        "version": 1
    },
    "errors": [
        "CPanel::Exception::API::NonExistent/(XID 123abc) The system could not find the “user123” user."
    ]
}

This frequently happens when a preceding API call (e.g., creating a subdomain or changing a PHP version) for the same account on the same server hasn't fully propagated or committed its changes internally before the subsequent API call attempts to modify it, even after introducing a short delay.

What are the best practices or known workarounds for ensuring atomicity and consistency when performing rapid, sequential WHM API operations on cPanel accounts, especially in a high-throughput automated infrastructure hosting environment? Are there specific WHM API internal queues or locking mechanisms we should be aware of, or perhaps a more robust method for validating an account's 'readiness' after a modification before issuing the next command?