Summary

When Swimlanes are based on Epics and there are Issues linked to Epics which are not available in the board, then these Issues are still visible in Backlog (for Scrum) & Kanban Backlog (Kanban) but invisible in Active Sprints (both Scrum and Kanban)

Steps to reproduce

1. Create board A (Scrum) for project A, which should filter all issues in project A
2. Create project B, then create Epic B in project B
3. Create Issue A in project A, then link it to Epic B
4. Create a sprint in board A, add Issue A to it and start it
5. Configure board A and base Swimlanes on Epics

Expected behavior

Issue A is visible in Active Sprints of board A

Actual behavior

Issue A is invisible in Active Sprints of board A

In Backlog mode, all the 4 issues are visible

The workaround suggested elsewhere is to change the Saved Filter to:
project = "This Project" OR ( project = Epics AND type = epic ) ORDER BY Rank ASC