XCFramework "Cannot load underlying module"

I've built an SDK (which has dependencies) and packaged it up as an XCFramework for clients' use, but when I test it in a project, I'm getting:

...SDK.swiftmodule/arm64-apple-ios.swiftinterface:20:8: Cannot load underlying module for...

This occurs in the Compile Swift Sources action and the break is in the import DepedencySDK statement in the swiftinterface file

In the SDK project and the demo, the dependencies are loaded into the project via cocoapods.

Any ideas? Or suggestions on how to debug this further?

Thanks!