There is a problem affecting all UK Marketplace applications, this includes QuestionWhere, MyNearest, Markr and Sweet, which appears to have been introduced by yesterday's ArcGIS Online update.
The problem results in the applications not loading.
Esri UK are investigating the issue as a priority and working directly with Esri Inc to get the problem resolved as soon as possible.
The problem has now been resolved and all applications should be working as normal. Please contact Esri UK Technical Support if you experience any further problems