Only "[object Object]" entries in the web app for alerts for the "Assigned to" field in TFS2015

Hi,

since the upgrade from TFS 2013 to 2015 the "Assigned To" field in the alerts are only showing [object Object] instead of the usernames. See image. 

In the WI the assign to field works more or the less fine, although the users domain name <domain/username> is added in VS2015 but is missing in the web app,... 

Any idea?

gernot