Android Split Binary - Failed to resolve packages: fetch failed with status code 5

My .apk is over 100mb, and so I need to split it. I read that in 2015, this capability was added to Cloud Build (https://blogs.unity3d.com/2015/09/24/unite-2015-new-features-for-unity-cloud-build/).

I took an existing working build and went to Config > Advanced > Split Application Binary = true w/ Unity (2018.1 Latest). When I run it, the build fails quickly with the following error:

68: [Unity] DisplayProgressbar: Unity Package Manager
69: [Unity] [Package Manager] Registering 0 packages:
70: [Unity] Failed to resolve packages: fetch failed with status code 502. No packages loaded.
71: [Unity] A re-import of the project may be required to fix the issue or a manual modification of /BUILD_PATH/eric-farraro.krumit.android-release/Packages/manifest.json file.
72: [Unity] (Filename: Line: 0)
73: [Unity] [Package Manager] Failed to resolve packages: fetch failed with status code 502.

Things I've tried:

• Rebuild same build
• Uncheck 'Split Application Binary' - build works again
• Clean Build

As far as I can tell, the only difference is this Split Application Binary toggle. Again - the build works 100% of the time without this toggle selected.

Has anyone gotten .apk / .obb split builds to work in Cloud Build and/or can anyone on the Unity team help take a look?