SwiftPM in Xcode 16 unable to clone package repository that can be cloned manually

Hello all,

I have an Xcode project that depends on the package at GitHub - maitbayev/iosMath: Beautiful math equation rendering on iOS and MacOS.

When I loaded the project in Xcode 16 beta (16A5171c), it failed to resolve the package graph with an unusual error:

the package manifest at '/Users/nicholashubbard/Library/Developer/Xcode/DerivedData/Sort_Symphony-abajgqcxhjqghcejmgkqfofzqoxh/SourcePackages/checkouts/iosMath/Package.swift' cannot be accessed (/Users/nicholashubbard/Library/Developer/Xcode/DerivedData/Sort_Symphony-abajgqcxhjqghcejmgkqfofzqoxh/SourcePackages/checkouts/iosMath/Package.swift doesn't exist in file system)

This is all the detail I was able to get out of Xcode; all of the other errors reported were related to not being able to resolve the package graph because of this specific error.

The repository does have a Package.swift file, and it appears to be valid. So I checked the folder where it tried to clone, and the only content in the folder was two root-level folders from the repository (iosMathExample and iosMathTests), both with no files.

Why would Swift package manager or Xcode fail to clone this repository, despite it being publicly available and able to be manually cloned?