I have the same phone and got the Samsung system update Saturday. I don't know if the update is causing the issue because I only noticed it this afternoon, two days after the update.
BUT IT'S NOT JUST AQUAMAIL. I can open AquaMail, but not the messages. I also cannot open GMail, Audible, Kindle, New York Times, Washington Post, Dropbox, many or most apps on my phone that are dependent to some extent on an internet connection. Most apps that have no need of internet seem to open and operate normally. But it's odd, OneDrive and Google Drive work fine, but Dropbox won't.
And my internet connection itself is ok, and some internet connected apps do work. Strange
I'm going to call Samsung tomorrow and see if they have any ideas. I was figuring on a factory reset. But if others are having the same issue, maybe a factory reset won't help.