Why the field name for my date field has changed?

the odd part it I have seen it change a few times from what I thought it was and then go back and it is something else. Why would this happen ?

The name is set up based on the label you set to the field, for example, if your field is label it as "Date2" the name should be "date2".

The name may be different if you have two fields with the same label, so it assigns the same name, but adds the field ID to avoid confusion, currently the field on your form is labeled as "Date2", but the name shows as "date2127".

So for example, if you update the field's label the name will be changed to that, here is a screen-cast as example: 

So the field's name should not change if you do not change the label on it, otherwise it will be changed too.