NetTcp retransmissions

Using a NetCore server as per https://github.com/CoreWCF/samples/tree/main/Scenarios/Getting-Started-with-CoreWCF/NetCoreServer and a Framework client as per https://github.com/CoreWCF/samples/tree/main/Scenarios/Getting-Started-with-CoreWCF/NetFrameworkClient both on the same windows 10 20H2 workstation. The server is configured as windows service:

var builder = Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(w => w.UseStartup());

builder.ConfigureWebHost(w => w.UseKestrel());
builder.ConfigureWebHost(w => w.UseNetTcp(rti.Port));

builder.UseWindowsService();

builder.Build().Run();

When first calling the server it takes about 5 seconds to get an answer. Subsequent request are answered in a few milliseconds. After some time without making a request this behavior repeats.

Wiresharking the first request gives the following:


Obviously this is not a workable situation but I'm kinda lost here. What am I doing wrong?