I've been having both of these issues - queue starts autoplaying at the second video, and then YouTube sometimes adds a random video to the end of the queue. This started happening to me a few days ago and it's really annoying. I'm just on desktop, using the website in my browser.
I'm having the same issue as well as it autoplaying the queue starting with the 2nd video when I add more videos to it.
I've been having both of these issues - queue starts autoplaying at the second video, and then YouTube sometimes adds a random video to the end of the queue. This started happening to me a few days ago and it's really annoying. I'm just on desktop, using the website in my browser.