Steps to reproduce: Same as Unreal Engine Issues and Bug Tracker (UE-76517), however, the final camera cut (on leaving the sequencer) must have ViewTarget == LastViewTarget (easiest to see if there is a single shot sequence, targetting the same actor as the player)
In LevelSequencePlayer.cpp (line 297) there’s a section where bRestoreAspectRatioConstraint is set to true, but immediately after, it’s possible to early return before ever restoring the value.