I just ran into an issue with a ESRI tech representative where we spent hours on the phone just to realize the issue was with AGOL. If you have the following option checked within your Organization > Edit Settings > Map > 'Use ESRI vector basemaps in supported ArcGIS app' then when you try to create a map for download capabilities you are unable to do so. I created a standard map with just one layer containing OFFLINE capabilities and we couldn't figure out why it wouldn't work. With this feature turned on, ESRI sneakily adds a topographic basemap layer that is 'vector' under the basemaps group. Worst yet, AGOL provides no feedback whatsoever that the issue lies with the basemap. Either AGOL needs to provide a log/prompt telling you which layers are not properly set up for OFFLINE capabilities OR automatically remove the vector layer when publishing a map that contains 100% OFFLINE capable layers and the user click the OFFLINE mode on.