What is the version of xEdit you are using?
SSEEdit 4.0.2m RC1 for 4.0.3 (10A4DD4C) starting session 2019-11-18 23:07:22

Describe the bug
There is an ambiguity in the PACK definition for Skyrim. ANAM subrecords can belong to either the Package Data\Data Input Values section or the Procedure Tree\Branches section, and if there are no subrecords between the two, it becomes impossible to add any to the Procedure Tree\Branches section.

To reproduce

1. Make a new PACK in xEdit
2. Add a Package Data section
3. Add a Procedure Tree section
4. Save and relaunch - notice that you now have two Package Data\Data Input Values entries, and that the CITC subrecord is now misplaced:

Error: record PACK contains unexpected (or out of order) subrecord CITC 43544943
Errors were found in: [PACK:01000801]
Contained subrecords: PKDT PSDT PKCU ANAM ANAM CITC 

Expected behavior
Creating a new PACK in the CK creates the XNAM - Marker subrecord (as well as the OnBegin, OnEnd and OnChange sections), so that subrecord should probably be required.