So I just recently got the bug where the chest in the middle of the timelines doesn’t activate or show you the cutscene. Here is the fix for anyone in the future that needs it:
Run to the chest and stand next to it. Open your map and click on the “Age of Winter” timeline, although this might work with clicking any of the other timelines. As soon as you do that and before it warps you there it will unlock the chest. After that you’ll warp over to the Age of Winter timeline and then you’ll have the blinking circle over the chest on your minimap to run over to.
Hope this helps someone.