Symptoms

K2 ViewFlow shows endless spinner and no errors.

 

Diagnoses

This happens when ViewFlow parameter "?ProcessID" specified in lower case, i,e.

This URL works:
https://k2url/ViewFlow/ViewFlow.aspx?ProcessID=XXX
But this one does not - and show endless spinner:
'https://k2url/ViewFlow/ViewFlow.aspx?processid=XXX

You can see this behavior in all current versions of K2 (up to 4.7).
 

Resolution

Make sure you don't use lowercase for "?ProcessID" parameter as this parameter is case sensitive.