Update:
It is NOT WebXR per se. It has something to do with rendering my second camera (as in this thread WebXR render canvas and streaming - #24 by MarkM ). When I start XR I add another renderFunction to the render loop which essentially changes the activeCamera, calls render(false, true) then changes the active camera back. If I disable this function then the performance is fine and scene.animate reports approx 5ms.
You can see the second scene.render in the screenshot in the previous post, it does not cause scene.animate to be called (as expected as second parameter ignoreAnimations=true) but it causes a blow out in the time for scene.animate in the PREVIOUS render?? (unless it is just the way dev tools is reporting it).
I feel like it is high time I tried to recreate this in a PG 