I face this issue, when I restart my code editor and continue my to project, but every time when I am trying to add new classes of tailwind which I had not use in previously, its not working, but also when I apply the same class which I used in previous lines its worked.
simple and working solution go on tailwind official website and open documentation, npx tailwindcss -i ./src/input.css -o ./src/output.css --watch find this command and modify it according to your CSS folder structure, after that paste in your terminal and just hit the enter button and you find your server start now use.