From the patch notes
In order to maintain the difficulty of certain duties, item level sync has been applied to the following dungeons:
The Wanderer's Palace
Amdapor Keep
Pharos Sirius
Copperbell Mines (Hard)
Haukke Manor (Hard)
The Lost City of Amdapor
Halatali (Hard)
Brayflox's Longstop (Hard)
Hullbreaker Isle
The Tam-Tara Deepcroft (Hard)
The Stone Vigil (Hard)
Item Level Sync 110
Looks like it won't be optional