Apple TV 4k + Tacx Neo 2T; everything up to date including trainer firmware; wasn’t using ZC, but that is also up do date; just rode Alpe du Zwift (doing a Med SST workout); very close to the start of the route (not the climb), just after the windmill as the road starts going downhill, there was a massive boulder / rock formation / grey slab on the right side of the road jutting half way out into the road. Did not block my path, but very nearly. Didn’t get a screenshot of it 
Everything else on route was AOK.