xcodebuild and swift package manager, can't resolve package graphs

TLDR: how can I get Resolve Package Graphs to succeed when running Xcode 16 under Fastlane? Is there some option to scan I am missing or some setup/config I need to do prior to running scan?

My company is using Fastlane to run tests when we open PR's. It's failing while trying to resolve package graphs for SPM / Swift Package Manager packages.

With Xcode 15, this runs great:

    desc """
        Builds a Debug configuration of the app and runs its tests.
        - Example usage: `fastlane test`
    """
    lane :test do
        puts(message: "about to scan for tests ☺️")
        scan(
            workspace: "MyWonderfulApp.xcworkspace",
            scheme: "MyWonderfulApp",
            configuration: "Debug",
            cloned_source_packages_path: "~/SourcePackages",
            clean: true,
            reset_simulator: true,
            device: "iPhone 15" - or "iPhone 16" if we're under Xcode 16
        )
        puts(message: "done scanning for tests")
    end

And the log looks something like this:

[16:29:47]: Driving the lane 'ios test' 🚀
[16:29:47]: ------------------
[16:29:47]: --- Step: scan ---
[16:29:47]: ------------------
[16:29:47]: Resolving Swift Package Manager dependencies...
[16:29:47]: $ xcodebuild -resolvePackageDependencies -workspace MyGreatApp.xcworkspace -scheme MyGreatApp -configuration Debug -clonedSourcePackagesDirPath \~/SourcePackages
[16:29:47]: ▸ Command line invocation:
[16:29:47]: ▸     /Applications/Xcode_15.4.app/Contents/Developer/usr/bin/xcodebuild -resolvePackageDependencies -workspace MyGreatApp.xcworkspace -scheme MyGreatApp -configuration Debug -clonedSourcePackagesDirPath "~/SourcePackages"
[16:29:47]: ▸ User defaults from command line:
[16:29:47]: ▸     IDEClonedSourcePackagesDirPathOverride = /Users/runner/SourcePackages
[16:29:47]: ▸     IDEPackageSupportUseBuiltinSCM = YES
[16:29:52]: ▸ Resolve Package Graph /
[16:29:52]: ▸ Fetching from [email protected]:mycompany-dot-com/ios-xc-alamofire.git
[16:29:55]: ▸ Fetching from https://github.com/Salesforce-Async-Messaging/Swift-Package-ServiceChat
...
...
[16:31:58]: ▸ Checking out 7.13.3 of package ‘GoogleUtilities’
[16:32:19]: ▸ Resolved source packages:
[16:32:19]: ▸   swift-snapshot-testing: https://github.com/pointfreeco/swift-snapshot-testing @ 1.18.0
...
...

With Xcode 16 however, we never get to the "Resolved source packages" line in the console log. It times out after our default timeout of 40 or even 60 minutes.

[16:57:37]: ▸ Command line invocation:
[16:57:37]: ▸ /Applications/Xcode_16.2.app/Contents/Developer/usr/bin/xcodebuild -resolvePackageDependencies -onlyUsePackageVersionsFromResolvedFile
[16:57:37]: ▸ User defaults from command line:
[16:57:37]: ▸ IDEPackageOnlyUseVersionsFromResolvedFile = YES
[16:57:37]: ▸ IDEPackageSupportUseBuiltinSCM = YES
[16:57:40]: ▸ Resolve Package Graph
[16:57:40]: ▸ Fetching from https://github.com/Veriff/veriff-ios-spm/
...
...
...
[16:58:29]: ▸ Creating working copy of package ‘swift-syntax’
[16:58:29]: ▸ Checking out 510.0.2 of package ‘swift-syntax’
Error: The operation was canceled. // 40 to 60 minutes later, due to timeout

I've seen similar questions to this posted elsewhere, with no answers. Hopefully somebody somewhere has jumped over and solve this problem.