For other’s who come across this problem … there is also a finicky problem when mixing 2d layers inside 3d layers, make sure all layers are 3d (although 2d layers in the background seem to function fine).
Funny story > recently I came across a layer that was disappearing when rendering and nothing I did fixed it. Only after many hours of hair tearing I found out I’d somehow enabled the GUIDE LAYER option. 🙁