Sorry for bringing up the old thread - I am trying to use a VTV on Cocoa and facing the same issue.
Using Lazarus/Cocoa built by fpcupdeluxe from FPC fixes_3_2 and Lazarus fixes 2_0. Then adding the VTV package (virtualtreeview, not virtualtreeviewonline).
In my test app on Cocoa the same thing happens: toolbar buttons disappear until clicked, some edits get clipped or misplaced, etc.
I wonder if it was solved or there is a workaround for now?