Hdri backdrop and Gi is broken?

Can someone pls explain this to me - I drop an hdri backdrop in my scene and a ppv to control some aspects of the raytracing. I see no Global illumination whatever I do so I go and insert a directional light again no GI visible…when I hide the hdri backdrop my Gi is visible and controllable? Is this broken? or is there something else I’m missing…

@Miguel1900 it turn out you only need to set the HDRI material blending mode to masked and it worked for me, this is my video using HDRIbackdrop you can see the reflection and GI working fine.