All tasks under Epic seems could not adjust time duration and it is locked for the entire sprint when the task is assigned to a Sprint.
Have a look at GIF below only the EPIC WOZI-1 time range could be adjusted, all other sub-tasks under the Epic, the timeframe or duration could not be changed at all.

I tried to assign a Start and Due date for each task but it does not seem to change the duration at all in the Roadmap.
To provide more context, all tasks are assigned to the current Sprint "v1.3". It is a 2-week Sprint. If I shorten the duration for an Epic an (!) would show next to it says "childs issue start and end outside"


