Some manner of collision hull does not seem to move out of the way when the fireplace secret entrance mesh that is cassmhallfireplaceex01.nif is opened. As such, it makes passage through it impossible, requiring disabling through the console. Dawnguard main quest progression requires passing through two gamespace instances of this mesh.
Fix was reapplied on vanilla mesh, as the previous fixed mesh in 35887 had other alterations to it that required starting from the original, one of which may have been the culprit.
Attached mesh goes in meshes\dlc01\dungeons\castle\animated\fireplace\
Attached Files:
cassmhallfireplaceex01.nif
Issue Data
Issue #36307: Animation collision issue in 35887 makes passage through mesh impossible