When changing the ownership of an item in ArcGIS Online, the item remains shared to groups the new owner is not a part of despite the new owner removing all sharing of the item.
Any group owner or group manager can add any public or organization level content to the groups they own or manage because the items are shared with everyone or the entire organization. The item owner does not have the capability to remove their own items from any of these groups when the groups are not his or hers to manage. Item owner can only see his or her groups (as a regular member, a group manager or group owner) listed at the edit group sharing.
解决办法
Join the group and remove the item from the group's Contents page.
Ask the member of the group with appropriate permissions to delete the item from the group's Contents page.