&1 &2: Moved to the end of its collection

What causes this issue?

You dragged a project element and dropped it outside of its collection.
This is not allowed.
Example:
,,...
,,Phase1
,,,,Task 11
,,,,Task 12
,,,,Task 13
,,,,Checklist 11
,,,,Checklist 12
,,Phase 2
,,...
,,You dragged task 12 and dropped it between checklist 11 and checklist
12.

System Response

The system moves the project element to the end of its collection.
Example:
,,...
,,Phase1
,,,,Task 11
,,,,Task 13
,,,,Task 12
,,,,Checklist 11
,,,,Checklist 12
,,Phase 2
,,...

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.