Management tends to push high-level epics straight into Scrum teams with the help of willing PO and weak Scrum Master. With the effect, that the team is drowned by questions, unresolved dependencies and half done requirements. Missing acceptance criteria opens the door for technically driven assumptions and overengineering. With UX and design missing, the already slow team runs into changes after each sprint, when stakeholders, confronted with first results, realize what they really want and how it should look like.
Try to prioritize on an epic level. You can do this with Moscow, Stacey diagram, value-effort/risk diagram or return on investment-effort analysis. Break epics down into features and prioritize again. Align with all teams, identify dependencies, negotiate API and gather all information that is required to make the features ready for implementation. If readiness has been achieved and stories are written, start implementing. The team should now be able to implement the feature fast and to get feedback on a first increment, that delivers the first function to a client. If the organization sticks to this workflow, features can be delivered fast and respond quickly to internal or external drivers for change.