What columns do you have added to the default view for the library? I've seen issues like this before when I had forgotten to add the columns I wanted to the default view. It seems unlikely Title wouldn't be in there, though...
I also saw a similar SO question where the .load function uses an extra argument:
clientContext.load(collListItem, "Include(Title)");
You might want to try that out as well, though honestly I've never used that second argument before.