Customizing font size in body of the timeline interaction reverts back to very light grey, small default font when published. It has allowed me to customize fonts in previous interactions. It does however, take multiple attempts to change the default font size in the customize option, changing to 16 pt font, it will default from 10 to 30. The light grey font is very difficult to read when published.
This seems to be a bug with Timeline interaction.
Sorry for the inconvenience. We will try to address this in the coming releases.
Adobe Presenter Engineering Team