I just tried the following. It seems to work for me.
Created a project.
Dropped a TP4 media generator event onto the timeline.
Changed "Enter text" to "Type on text, type on text"
Added type on transition animation. 2 seconds.
The TP4 timeline length was 6 seconds. more on this later.
Played fine in Vegas.
Save project. Close vegas. Open project.
Older versions of TP3/TP4 automatically adjusted their event length to the Vegas media generator length. Now you have to manually adjust this per event in TP4. What a pain.
So double check you Vegas media length, event length and make sure the TP4 length matched the media length. If you have type on as an out transition and the event length is short compared to the TP4 timeline, then you will not see it.