US visa control is the absolute worst!
Many years ago I worked for a startup as their primary technical guy (building servers to burn mix CDs in physical shops just before MP3s really took off.
We were working with Loblaws in Canada and Best Buy in the US with exclusive deals.
Our main datacentre was in Toronto and myself and a UK and US colleague were sent over there to build servers from parts. We were sent for an unspecified amount of time without return tickets which turned out to be 3 weeks. Just before leaving there was a problem reported from the Best Buy HQ about their test servers so I got shipped to Minnesota to fix.
Was probably a day or twos work, but we had no idea what the issue was.
I got collared whilst trying to enter the US and pulled into a meeting with immigration. I had everything I needed, including a letter from Best Buy, a letter from my company, hotel details, etc. What I didn't have was a return date!
I had to prove that the 2 laptops I was carrying worked, I had to show them the data I was transporting on 3 external drives and then I had to argue with them for a couple of hours as to why I had to do the work and no-one from the US could carry out the work. That was the major sticking point even though that due to the proprietary nature of the setup I was the only person in the world qualified to work on the issue and that the CEO of best buy had requested that I personally came to fix things. They finally let me in and it took about 1 hour to fix the issue and then I had to return (albeit via toronto again and I has to spend an overnight stay in the deserted airport which was quite spooky!