[itsme]

the line
%%vocalfont Helvetica 18 
was the culprit

It's just about the size, with
%%vocalfont Helvetica 14
it's OK, with
%%vocalfont Helvetica 16
the issue occurs.

So, just guessing, increasing vocalfont makes the ABC section too big / wide / whatever, it doesn't fit onto the page and this is why it isn't shown at all.
This can happen anyway, I came across that effect before, but can't remember when and where. It's just ugly and inconvenient that there's no feedback or error message. If there could be an error message like 'ABC section too wide / high / large' or the like, it would be good hint what I need to change to avoid that.