LiveReload All The Things not working

Hi, I work with ionic 4 and I have read this part of ionic article

One of the best features of the CLI is the LiveReload server that gets started when you runionic serve. This allows you to develop your app in the browser and have it update instantly when changes are made to any development files.

But this is not true. I use ionic serve.
After I change some files, 90% of times ionic serve not recompiling nothing and when recompiling I have to wait 20 sec every time!!!