The fairy lights will z-fight with the vanilla fence model's connection elements when connected through it in parallel and the camera is far enough away for depth inprecision to occur.

Mod version: 2.1.2-1.12.x
Forge version: 1.12.2-14.23.4.2744

I also notice a rendering issue regarding the translucency against the fluid renderer, although I believe that to be an issue with vanilla and not this mod. I can open a ticket for it regardless, if you want.

Closing as by design no restrictions are imposed on strand positioning and as such there are endless z-fighting chances.