The fact that the UIKit module (which is part of the SDK and thus should always be available) couldn't be imported indicates that there is likely an earlier error that's the root cause for this. Could you run the failing expression followed by (lldb) swift-health-check and create a FB with the result?

Responding to the comment about static frameworks: An unintuitive property of static libraries is that if you are producing a static archive that contains Swift code, the build system does not keep track of the associated .swiftmodule files, because they are separate artifacts from the .a archive. In this case you need to manually add -add_ast_path /path/to/mystaticarchive.swiftmodule to the linker flags of every binary or dylib that links against the static archive.

If you can reproduce this, could you add log enable lldb types -v -f /tmp/types.log to ~/.lldbinit-Xcode, restart Xcode, and reproduce the issue and then file a feedback with the /tmp/types.log log file?