Thanks for writing.
The plugin no longer uses the default Leaflet popups because it was difficult to get them to resize properly. Instead, I’ve switched to the custom ‘InfoBox’ popups for both Leaflet and Google. Those use a slightly different div structure. If you check the /css/mappress.css file in the plugin directory, it contains an overview of how the divs are nested.
I’m sorry for any inconvenience, and I hope that helps.