Not sure if this is the right place for this but since the New Year, the way Amazon.com has worked has changed for me. Suddenly I have to reselect my address (I have a couple of addresses on file because I have shipped gifts direct to friends) and the credit card I use and then I get the summary screen every time I place an order. I used to just get the summary screen (where I can make changes) and that was it. Did anyone else see a change how the orders are placed recently?
Nope. It’s asked me to reselect my address every order for years now, ever since I ordered something for an aunt for her birthday three or four years ago. I wonder why you haven’t had to until now.
Interesting. I guess I was lucky for a long long time and my luck ran out. 
You might try going into your account setting and selecting a default ship to address.
Changed for me, too - I think it was last month or so when it finally decided “oh hey, maybe you want to ship to these places you haven’t sent anything to in years?”