Apple rewrote the whole layout and text framework used by Cocoa views. The rewrite was incremental, so some features were not yet available on some previous macOS versions, and some behaviours may differ.
Anyway, setting a layout manager makes it use the old layout and text framework, so you will have the same behaviour as in older macOS versions. You can either try to find a way to get the wanted behaviour with the new framework, or keep using the old one for now I guess.
I think there is some info on the AppKit release notes and in various WWDC sessions.