Download png button not working in shiny app

Hi:

I've developed a Shiny app that uses Plotly. I've been reported several times a problem when exporting plotly plots that I am not able to solve and, even worse, I am not able to reproduce.

The app is at my github account (it's called memapp) and also at CRAN repositories, plots are ggplots coverted to plotly using ggplotly and rendered with renderPlotly.

This is the exporting window as usual, only available format is png, the image is correct:

http://ibb.co/h3Kyrn

But in some systems, when people try to export a plot, the window turns to this one, only svg vectorial file available.

http://ibb.co/jEi2HS

The exported image is not readable, at least by some online software I've tried.

This is the pastebin of the svg file:

https://pastebin.com/a3CLDTYN

My app is hosted online on a server running linux, this error happens when they run the app locally or at my server, so I guess it is not a problem of my app and it is something dependent on the OS of the client. People reporting this problem uses Windows OS (10 for sure, 7 or 8 I am not sure 100%).

Any clues of what's happening? What does Plotly check when exporting to png or svg files that can make certain systems not to allow to export to png?

Inizia riproducendo il comportamento di esportazione nell’applicazione Shiny memapp, concentrandoti sui grafici convertiti con ggplotly e renderizzati con renderPlotly. Confronta il comportamento di esportazione di PNG e SVG sui sistemi Windows indicati utilizzando gli screenshot collegati e il pastebin SVG; il lavoro è completato quando viene identificata una causa riproducibile o una limitazione di esportazione documentata.