I had the same issue importing with the @ alias, but the above did not resolve my issue.

What resolved it for me was actually in the Vercel Project Settings, I had set the Build & Development Settings to 'npm run build' and set the override to enabled. Vercel must be messing with something when you do an override as the build command they show in the logs is the same as I put in the override.

After disabling this override, when the deploy ran again the imports that used the @ worked.