Actually, the idea is:

1 there is a master_categories_id set on the Product

2 the products_price_sorter is up to date

3 Starting at Price uses the lowest price in each Attribute Option Name Group based on who is marked to be Include in Base Price in the Attributes Controller
By Default, this is figured out for you and you should not have to exclude any of the Attributes from this
Only if you want to alter the automatic calculation of the Starting At Price, would you ever need to change the default setting (YES) for:
Include in Base Price
When Priced by Attributes
Edit the default attribute selection price, save, update, Starting At price displayed changed to lowest priced attribute.
Setting the Default Attribute should have no affect to the Starting At price ...

If doing that fixed it, try and Edit/Update with no changes, does that also fix it?