The Esri default basemaps are not shared to custom portal groups if only the 'Share Esri basemaps to the group' check box is checked on the Settings tab before clicking Save.

Additional Information

Workaround

Perform another action on the page before clicking Save (for example, using the drop-down list to choose the group). If the group is already selected, switch back to the Esri default settings, click Save, then use the drop-down list and the check box together on the next save.

Steps to Reproduce