Auto Lip Sync - can't choose all graphic symbols

Hi,

I am using the Animate lip sync function for the first time (total novice at animate cc anyway), and have created the graphic symbols etc., and can see them on my timeline and in the library.  They are definitely graphic symbols not movie etc.,.

When I then select the track and frames I want sync,  it doesn't give me a choise of the various 12 frames to be able to allocate to the sound shapes.

I'm obviously doing something wrong, and probably straight forward.  Any help greatly appreciated.

Many thanks.

Martyn.