Custom noteheads in iOS app

Hello,

I have created a drums score which incorporates pictograms of the different elements as noteheads (this is for a child with autism who needs explicit visual cues). As you can see on the attached screenshots, I have added those symbols to my custom palette and pasted them over the original noteheads, which I've turned invisible.

While this works fine in the desktop app and on the website, the symbols do not show in the iOS app that the child uses on his iPad — only the stems.

Is there anything that can be done about that ?

Thanks in advance.