Hi Robin,
Those animated items in Video annotations are prebuilt motion graphics with a fixed animation length. Stretching the clip or using Edit duration does not extend the underlying animation, so they stop even if the timeline bar is longer.
A simple way to keep one on screen longer is to chain duplicates so the animation immediately plays again with a soft join.
Select the annotation on the timeline and press Ctrl+C then Ctrl+V. Drag the copy so it touches the end of the first one. Open the Transitions tab, drop Crossfade between the two, then shorten the transition to a very small value so the loop feels seamless. Repeat the copy and crossfade as many times as you need to reach the total duration you want.
If you tell me the exact annotation you are using I can suggest the transition length that hides the restart best.