Hi Emme,
R15, R16, R17, all have the same option to go into Legacy Mode, hence the same dynamically mode if legacy is off. I checked all three. Same text in the Help Content.
I have to admit, I’m confused now, so I can’t point you to something that could clear it for you. Perhaps more information?
Menu>Editor View>Options>Configure All…
Attribute Manager>Back>Legacy Mode OFF.
All the best