Is it possible to turn on HTTP Proxy on a domain and still use a GRPC protocol towards that domain?

Background: I have a website on and a GRPC API on
When I turn on HTTP Proxy for the domain the GRPC client (outside mydomain) always returns an Internal error (when trying to reach mydomain) with a description of “server closed the stream without sending trailers”.

PS. When turning off HTTP Proxy and use CF for DNS only, everything works fine.

Any ideas?