When you have multiple tracking sources, it’s important to keep the position of those sources in mind.
Position is required only for online sources. As you can see above, there is a source for Ad Extension that has no position, but it is not set as an online source.
Position is the order in which you want the tracking script to try and match your visitor to a source. So, for example, a visitor coming from Google organic could technically be a referral visitor and/or a google organic visitor. You always want the more specific source to be matched first so that a more generic source like “referral” does not swap first. The closer to 1 value in the position field, the higher the priority it will have in swapping. In the case of Referral and Google Organic, you would want Google Organic to have a smaller number so that it swaps before Referral.
To change the position, click on edit next to an online source then scroll to where you see Position. You can edit that text box.