Anyone else have issues with spider webbing in the paint? I have some starting on the passenger side bumper below the headlight right by the grille.

 

Whoa! That is beyond just average paint spider webbing/swirling. That's actual cracking of the paint/clearcoat. This can occur if the plastic was repaired at a shop and improper fillers etc were used. An elasticizing agent is needed when repairing and painting plastic fenders, bumpers and the like. If this isn't the after effects of a repair, then I'd go see Lexus for and answer and perhaps, resolution.

 

It's possible someone backed into you slowly and pushed the bumper in without deforming or making a impact mark.

 

I used to paint cars .. looks like a low speed impact that didn't leave any marks other than cracking the paint. If the bumper itself is in good shape the paint would need to be sanded off the cracked area and entire bumper repainted.

My back bumper has some cracking similar to yours probably from previous owner backing into something