My custom map uses this syntax:
${SITE_GEOGRAPHY|mapSettings: “<the id of a web map here>”:5000 |size:600:400}
In case that's helpful (the use of a different web map adds an extra dimension too I guess).
Also in the last few days I had to check the bindings of the geopoint fields in the xlsform for the survey. Turned out I had my geopoint listed as a number, and it used to not be an issue but apparently Esri introduced stricter checking of these things recently, and I got an error similar to yours.
I hope either of these things help - I've been knee deep in similar issues the last few days!