@partyof5 You gave some helpful information; thank you. I did just look at my order and I was mistaken; two of the items not due to me until 1/2/18 are both shipped and sold by Amazon, so previously I would have expected those items in two days due to Prime. Maybe this is just Christmas backlog, as I can not think of another time where I did not receive a Prime item in two days. At least I knew before hitting complete order that these items would take longer.
An interesting read about Amazon Flex:
https://www.geekwire.com/2017/amazon-delivery-driver-like-work-tech-giants-citizen-package-brigade/
Just filed lost items claim. Not just this one, but also the 2nd one I re-ordered!