you can simplify your filter. Instead of a manual concatenation you could use a format specifier. The code of your filter would look like this:
return $filter('date')(value,'dd.MM.yyyy HH:mm')+' Uhr';
maybe this helps already.
Giri's question is in fact very valid: where does the date come from?
I tested it right now with a connection to a property of Thing and a service result from a Thing (both from External Data) and that worked for me.