[SalesForce] pagereference return null vs void

You can use the rerender attribute of the action button to limit the scope of the refresh. In this case you don't want the whole page to refresh, just the area inside your "Account Settings" section. Is that a pageblocksection?
If it is e.g. <apex:pageBlockSection id="AccountSetSection"...
Then your button could include rerender="AccountSetSection"

This class and VF page works just fine in my tests.

So there is something you are doing between iterations that is different or something on your page that is weird causing it. I would suggest to comment out everything and try it to see if it works, then uncomment sections at a time and test and see when it breaks then narrow it down from there.

Class:

public without sharing class MyClass{
    public MyClass(){

    }
    public void createRecord1(){
        account a = new account(name = 'Test');
        insert a;
    }
    public void createRecord2(){
        account b = new account(name = 'Test2');
        insert b;
    }
    public PageReference createRecords(){
        system.debug('inside pagereference');
        createRecord1();
        createRecord2();
       system.debug('about to exit pagereference');
       return null;
    } 

    public PageReference createRecords_two(){
        system.debug('inside pagereference two');
        account a = new account(name = 'Test');
        insert a;
        account b = new account(name = 'Test2');
        insert b;
        system.debug('about to exit pagereference');
        return null;
    }    
}

VF Page:

<apex:page controller="MyClass">

<apex:form >

<apex:commandButton action="{!createRecords}" value="ONE" rerender="msgs"/>
<apex:commandButton action="{!createRecords_two}" value="TWO" rerender="msgs"/>

</apex:form>


</apex:page>