Thread:Elledy92/@comment-26838855-20190425183005/@comment-2106279-20190502013428

Edward Zachary Sunrose wrote:

And they don't necessarily need to appear on the machine, much like how Tony and Steve weren't on the machine in New York when they went to New Jersey. However, it can be assumed that the machine needs to be on during the time they make the jump (which it was in 2023).

This backs up my theory that Steve appears on the bench when Bruce registers him traveling but the machine doesn't fully activate. You reappear on the machine when you make the jump back to prime timeline. When Tony and Steve went to New Jersey, they were not returning to the prime timeline, they were jumping back in time. When all the Avengers finished the Time Heist, they all ended up back on that platform.

Therefore Cap should have returned on the platform. Him not being there led to the belief that Cap's time travel to the past was within the same timeline. However, the Russos have since debunked this by stating that he did indeed cause an alternate timeline and then took the shield and jumped back into prime timeline 2023 after living out a life in the alternate.