What is the version of xEdit you are using?
FO3Edit 4.1.3b EXTREMELY EXPERIMENTAL (CDA61A13) starting session 2020-05-06 22:54:02
(Happens on 4.0.3b as well)

Describe the bug
QAC'ing the two DLCs listed above will cause the same bug as the disappearing Soul Cairn/Apocrypha in Skyrim.

To reproduce
Steps to reproduce the behavior:

1. QAC Anchorage.esm
2. cow DLC02BaileysCrossroads 0 0
3. Note that most of the worldspace is gone
4. QAC PointLookout.esm
5. cow DLC4Pointlookout 0 0
6. Note that most of the worldspace is gone

Expected behavior
QAC should apply Mark Modified to these two files, same as with Dawnguard.esm & Dragonborn.esm in Skyrim.

Screenshots