Chrome disables buttons and input elements when offline
I figured out what was going on with my own page -- somehow every time I hit the app in the home screen, it would go to the saved offline page from Chrome instead of trying to actually use my PWA, and those saved offline pages have their inputs disabled.
I had to go delete the saved web page from Chrome to get mine to work again.
I only noticed because I changed some text around and nothing was correctly updated.
Your seems code is ok. So it might be the set up of the sys.
check the google tutorialhttps://developers.google.com/web/fundamentals/codelabs/your-first-pwapp/?hl=en#download_the_code