500 is an internal server error. Are you able to look at the error logs to see if something is registering there?
Intermittent errors are often tricky to troubleshoot.
To get around this I might code the function that accesses the rest API to retry if the status returned is 500.
See my comment above
We do see that the log Activity is registering the 2 entries other than that we don't see anything else. Is it possible that there is some Node in the node clusters which is corrupted?
We have asked the process that are calling the RestAPI to add retry around their code as a way of avoiding these issues.
