Do you know at what step it fails?
I love model builder but I have found it to not always be reliable. For example, it loses setting for geoprocessing when I validate the model; therefore, it would not run correctly as a tool. Also I found field mapping sometimes gets dropped which doesn't provide expected results.
To solve this issue, I perfect the workflow in model builder than write it in python. Otherwise, I have to manually check some of the tools in model builder to make sure all parameters are filled out correctly and run it manually.
Good luck!
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