I think, it happed because AddStaticKeyPathAsync() method uses ConsulConfigSource.FormValidKey() which adds / character to the end.
In consul documentation path looks like /kv/:key.
https://demo.consul.io/v1/kv/hi - works
https://demo.consul.io/v1/kv/hi/ - not:(

update documentation on:

Running under the full IIS

dotnet/AspNetCore.Docs#1982 (comment)
https://docs.asp.net/en/latest/publishing/iis.html
https://msdn.microsoft.com/magazine/mt736459
aspnet/Announcements#172
https://www.strathweb.com/2015/12/running-asp-net-5-website-on-iis/

HTTPs

https://blogs.msdn.microsoft.com/webdev/2017/11/29/c

Example:

$ cat Example.kdl
@type Example : "exmp" {
}

Output:

$ bin/kdl -o ../kdl-out/ Example.kdl
libc++abi.dylib: terminating with uncaught exception of type std::logic_error: [kdl::sema::parser] Attempted to access lexeme beyond end of stream.
Abort trap: 6

It'd be nice if the message was something like Example.kdl:L2:1 - Expected ';' at end of file.