Incompatibility among multiple while loops

I am going to use KEITHLEY 2700 to read Multiple voltages. The program is designed as While loop -shown as loop (2), and it works fine itself. Now I am going to implement this program into another Routine, which includes While loop (1), Case structure and While loop (3).

The structure is attched.

Now the problem is that: when the case structure is true, loop (3) is supposed to run, but in reality due to the running of While loop (2), while loop (3) is not runing at all.

Is there any advice on this issue?

Thanks