Open new Project
Create Midi track
Add a few midi notes.
Open Score editor
from Symbols open Line/Trill
Select 8va option (Cursor changes to pencil)
Draw on Score - crashes CB.
Yes Cubase stays open but the Score an CB becomes unstable and unworkable (Most functionality is frozen).
It is possible to restart Cubase and continue working with the project.
The 8va was registered on the score (I think).
Another test.
I reopened the same project file in Cubase 10.5 and saved the Score as MXML.
Imported the file into Cubase 9.5 and the 8va was viewable and editable, but the layout was somewhat inconsistant with the layout from CB10.5 version.