I generated the responsive HTML5 output from a DITA map. The output is not opening to the first file in the map, but to a file later. The first file is the introduction to the guide which I created from DITA topics and assembled into a map, as I've done many times before and never had a problem. I can't find a setting to tell it to open to a specific page. I'm using Adobe FrameMaker 2019, version 188.8.131.521.
In the ditamap, are you using chunk option. We think this issue is related to DITA-OT as FM for ditamap generates a partial output first using DITA-OT and then goes ahead and post processes to give the look and feel as requried in the skin.