How debug Universal links
while installing the app with Xcode I got no logs referring to swcd in xCode
I implemented Universal Links manually, but situation was similar. Particularly I mentioned empty swcd process log while installing the app, and it turned out that most likely iOS didn't even try to download apple-app-site-association file, like if responsible process wasn't run. In my case device restart helped and deep-linking began to work.
Thus I think restarting device is one another step in troubleshooting when you are sure about all your setup.