Hard to tell without access to your data - but my hunch is that your markdown document is missing a library declaration. Are you loading {sf} or whatever package that provides support for the data format of your shared_data object?
If your question's been answered (even by you!), would you mind choosing a solution? It helps other people see which questions still need help, or find solutions if they have similar problems. Here’s how to do it:
To create an unrelated plot I had changed numeric values to factors and overlooked changing it back for the SharedData set required for Crosstalk and for the map to render. There was no need to define lat/long.... just a need to stop staring at the code and sleep!!! As soon as I read it again this morning I saw the error. Just want to add that flexdashboard and crosstalk are fantastic packages for those like me who were taught latin at school instead of java script.
Many thanks