WP Sush Load Balanced Environments

Not sure about how the WP Smush plugin works, but we have a load balanced environment. We upload images via Add New Post, and these in turn get uploaded to our S3 Bucket. However we are getting lots of errors "Error posting to API: 500 Internal Server Error" and then it works fine. Is this because the source file is not on the same server as that does the smushing and the load balancer is sending requests to alternative servers to where the source file may not reside. To get round this we are thinking of either creating a dedicated server for using WPAdmin, but think we will run into problems with Domains. Alternatively we could modify our HOSTS file for each client that accesses WP Admin. Any thoughts anyone has would be greatly appreciated.