How to use IIS URL Rewrite with gzip compression
Please refer :https://blogs.msdn.microsoft.com/friis/2016/08/25/iis-with-url-rewrite-as-a-reverse-proxy-part-2-dealing-with-500-52-status-codes/
Outbound rewrite rules cannot be applied when the content of the HTTP response is encoded ("gzip").
This is because the responses that are coming from the back end server are using HTTP Compression, and URL rewrite cannot modify a response that is already compressed. This causes a processing error for the outbound rule resulting in the 500.52 status code.