RRD4J refresh on Android app

When I try to look at a chart (rrd4j), I need to manually refresh my sitemap. Then I see direclty the chart.
Else (more then 1 minute), the charts simply won’t pop up. just an icon ‘image loading’…

This is only on my phone (android), through a pc (google chrome) it works normally.
Any suggestion what I can do?