This blog pertains to web maps and layer items that have both of these characteristics:
Web maps and layers authored with ArcGIS Online prior to the June 2016 update.
Contains polygon layers that are styled using Smart Mapping tools to adjust symbol size and/or outline width automatically based on scale
You also have the ability to automatically adjust the width of the outline of the polygon based on the current scale. Automatic sizing of polygon outline widths were also being represented using pixels rather than points.
If you created a web map or layer item in Online prior to the June update with layer styles that take advantage of automatic sizing based on scale, we recommend that you reauthor your web map. This process will resave your web map with the correct sizing values for consistent display in all ArcGIS clients. Here are the steps to reauthor your web map:
Open your web map or layer item
Click on "Change Style" in the layer menu for the polygon layer(s) that use automatic sizing of symbols. Note: You might want to write down the options you have selected so that you can easily reselect them in step 4.
Select a different style for your symbols than you originally had selected and click "Done."
Click "Change Style" again on the same layer and reselect the original styling options you had, and click "Done." Any options that were configured within the original style must be reconfigured.
Save your web map or layer item. Your web map will now have size represented using point values.