REST call fails on large body with PowerShell

We have developed a REST endpoint based on IIS. For connecting to, we have a internet facing F5 load balancer.
We have tested different scenarios and have an issue when sending body, larger than 60 KB.

While testing with Postman everything works as expected, independt of size (several MB).
When we try to integrate this in our scripts (PowerShell), we get an disconnect when sending larger information. After sending 60 KB the connection is closed by F5.

Is it possible to figure out what Postman is doing different? Body and header information are the same. We also used the Postman generated code, but same issue.

  1. What is the exact error you are getting?
  2. Are you sure there are no sticky cookies that Postman has saved and that are being sent with the request?