Which density function could be causing this?

I'm trying helping someone put together a dimension for their server and very rarely we get these long "rivers". The dimension only has one biome. The world is based on terralith, and I have customized some density functions to remove surface caves and such, but in the process something made these happen, though they are very rare. It seems to me that some function is misbehaving and generating a 0 or something. Does anyone have any idea which density function could be causing this? I mainly just changed the vanilla cavegen functions, not the terralith ones