Further analysis revelead that everytime you make a change to Blur Strength during PIE LGUI will call RemoveFromLGUIRenderer() (it calls the OnUnregister method that contains that call) on the post process component thereby removing it from the list of the hudPrimitives array that get rendered from the LGUIRenderer that’s why the blur will not render anymore.
Is it this intented to work like this? To me it seems a bug. I could try to fix it overriding the OnUnregister to let the background blur ro have and empty OnUnregister version of the virtual method but I’m not sure that it will be the correct solution. The call stack doesn’t tell me who call the OnUnregister. The only thing I know is it gets called as soon as I change the value of Blur Strength in the details panel of the backgroundblur actor in editor.