I know this post was along time ago but I have a solution. - Open the visualization tab of your hosted feature layer. - Configure the pop up of the layer. - Click configure attributes - Click on the field you wish to move and use the arrows on the right to move it up or down the order. - Once you are finished moving, hit ok 2x then save the layer. Your reordering of fields has now been made to the hosted feature layer itself and will be maintained in any map you now add it to!
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