Where does SCA grab the information for the “Expected back in stock” date? I thought it was based off the lead time of the item, but that doesn’t seem to be the case, as I’ve got a new item that should be using the default lead time (60 days), but the ETA online is 30 days from the day the PO was placed.

SCA does not show "Expected back in stock" date as OOTB. I guess you have a customization or extension on your website