Retrieving custom metadata fields from the Pendo back end

Hi everyone - I've searched the forum history and this doesn't seem to have been answered before.

I have user flows in my app where we gradually personalise the user experience more and more based on their activity. A simple way to think of this is to categorize them as 'users' or 'developers'. I have created a custom metadata field for this and each time they reach a crucial step I update their persona by calling 'pendo.identify(....)' and adding that.

So far so good...that shows up in the Pendo UI. But I also need to call this back when they start a new session and this is where the problem comes...getSerializedMetadata() is only returning the core metadata fields, not the custom one I added. Looking at the network flows in my browser I don't seem to be getting anyhing back from the server, only a local cache...

Does anyone know (given a valid account and visitor ID)  how to grab the rest of the metadata including custom fields from the server?