Hi, i had the same problem in UE5 with “Allow Cinematic Control” enable. When enters in camera view and comes back to viewport it keeps the FOV value as the Current Local Length of the cine camera actor.
I cannot disable “Allow Cinematic Control” because if it was disable i cannot use cinematic commands as shift+c to comeback to sequencer camera view but adjusting all the time viewport FOV is kind of annoying issue.
I was looking for a way to create a editor widget blueprint to just set viewport FOV 90 (Default FOV) but apparently the viewport camera its not a usual think to acess and changes his parameters.