Roadmap child epics do not respect changes to sort order

Release notes

Problem to solve

Once #350315 (closed) has been resolved, so child epics respect the selected sort order, there is another issue where the state for a parent epic is not cleared when changing the sort order.

This results in the root epics updating with the new sort order, but their children keep the order when the parents were first expanded.

existing
simplescreenrecorder-2022-01-18_23.06.58

Proposal

When changing the sort order, the Vue start needs clearing for children epics.