I’m gonna guess this is another of the LoD bugs. I seem to recall that kind of distance in front of you being where some shadows jump to highest resolution. Also looks similar to the speckled shadows bug that’s been around for months, see last screenshot here: Speckled shadow textures in all worlds - #5 by Dave_ZPCMR
Unfortunately Zwift don’t appear to give a toss about this kind of thing. They hope you’ll buy an Apple TV and forget about it.