Start Invert not populating for ~90% of pipes in dataset

I have a dataset with nearly 3000 pipes in it, that have the start and stop inverts identified. When I am doing the initial setup through modelbuilder, roughly 90% of the start inverts are populating as 0.000. Stop inverts appear to be populating without any issue. I've gone through the modelbuilder process several times and keep getting the same result.

Attached is a zipfile with the project files and the dataset. UPELEV attribute is start invert, DOWNELEV attribute is stop invert.