Steve,
This is a bug caused by the language in your AGOL/Portal organization being set to Korean. Most of the basemap names are in Korean:
We will fix this in the next release but for now you can work around this by selecting one of the Basemaps named in English (National Geographic or OpenStreetMap). Once the project has been opened in ArcGIS Pro you can switch the basemap in the project to whatever basemap you want to use.
Thanks,
jt