Made it safely to the USA, but not without a slight hiccup in Vienna.
When booking Malta to Chicago, I booked with Austrian Airlines. It was an Austrian Arlines flight operated by Air Malta from Malta to Vienna, and then Austrian from Vienna to Chicago. In Malta when I checked in, they printed me a boarding pass to Vienna, and also printed me a boarding pass for the Vienna to Chicago flight on Air Malta paper.
We landed at Vienna at 9:20 AM, and our flight to Chicago began boarding at 9:15 AM. We ran to our gate, only to be told that our boarding pass was no good! We had to go to the Austrian air and have our boarding passes reprinted on Austrian paper. Thankfully, the place we had to do this was only 10 gates away and we were able to make our flight, but if we had to go to another terminal or something we could have easily missed our flight.
This happened once before to me: around 2014 I was flying Alitalia to Rome out of Philadelphia, and my flight from Reagan to Philly was an Alitalia flight operated by I think US Airways. At Reagan I got boarding passes for the PHI -> Rome flight printed on US Airways paper. In Philly, I was told I could not board my Alitalia flight with this boarding pass and I needed to find the tiny Alitalia desk to get it reprinted.
What kind of weird bureaucratic rule did I run afoul of in these situations?