I was wondering if there is any chance to fix NAN errors in my render setup. (FG+IBL+areaLights with WOM_archlight shader; photographic lens shader on camera, 16bit half rgba)

the shader which produces NANs in my scene is the mip_matteShadow. the only usefull thing I found out so far is that by lowering the reflection samples on the matteShadow material the black NAN pixels become less in number. also the NANs only start to appear after the camera has passed a certain angle facing normal to the groundPlane which has applied the matteShadow. that means in a flat angle, when the camera has almost no x-rotation (looking up or down) no NANs appear.

I was asking myself if there are some settings on a more basic level like in the renderGlobals rather than in the shader to prevent from rendering NANs..? Also, is there any analytic procedure to debug NANs?