Hi Vivek,
Thank you for posting your concern.
The InternalApiError.UNEXPECTED_INTERNAL_API_ERROR could be due to a temporary issue in the servers or could be due to a bug. However, upon checking the log you provided, you are using ExperimentDiversionService which is currently not supported in AdWords API and it seems to be the cause of this error.
With this, could you try to use other service listed here and check if you encounter the same error? If the issue persists, so I can further investigate the issue, could you provide the complete SOAP request and response logs via Reply privately to author?
Regards,
Hiroyuki
Google Ads API Team