Hi Henk,
Greetings from Syncfusion support.
As mentioned in the SfKanban responsive documentation page, Kanban layouts are shown properly on mobile devices. We have ensured Kanban sample in Chrome dev tools in mobile mode in various mobile selections and ensured the sample is on the direct device, both Android with the Chrome browser and the iPhone with the Safari browser. Please find the below videos for Android and iPhone testing.
We suggest refreshing the page when switching from desktop mode to mobile mode using dev tools.
Please let us know if you have any further assistance.
Regards,
Buvana S