Hi! I had the same issue when setting up my site doriebarton.com using Signify Pro. What helped me was adjusting the logo size in the Customizer — sometimes, on mobile, the logo takes up the entire header space and pushes out the site title.

Try reducing the logo dimensions slightly, or upload a version optimized for mobile. In my case, once I adjusted that, the site title started showing up again.

Hope this helps!
— Dorie