Check out example codes for "il2cpp stuck unity". It will help you in understanding the concepts better.

Code Example 1

if you try to build to android and its stuck on "IL2CPP" or "Gradle"
  so make sure the game file saving on a place without letters on other language 
  or special letters like ""~`'\/., etc

Code Example 2

//save the folder on a place without words in other languages and no special keys

Code Example 3

If webGL build gets stuck here...
Windows Key + R
Type in "regedit"
Do this while it is stuck and it should start working again.

Learn ReactJs, React Native from