Code builder keeps freezing

I have been teaching the coding fundamentals lessons 1-3 lessons to students in my school.  I have had several students who keep having their code builder freeze in lessons 1.2, 1.3, 2.1, 2.2, 3.1, 3.2.  Do you have any fixes for this?  The wheel just spins and spins and we have to save and exit their lesson or sometimes restart the lesson to get to to reload.