After checking the problem over and over I realized, that I had overlooked a small detail while building my Interface.
This lead to me no longer needing the part i showed above, as it is. After moving everthing into different Blueprints, making/having different References, it all started working as intendet. So long story short, I´m no longer in the need of an answer. However, because I already opend this thread and there might be someone having the same problem, I decided to look into it once more. So I double checked my new Blueprint communication and compared it to the one posted above. And didnt seem to find differences except for the references beeing different and the WidgetBlueprint beeing spawned from a different WidgetBlueprint throug its Graphictab, as it is a part of said Blueprint. This problem migth be something that needs further checking, for people experiencing something similar.
Still my problem is solved, thanks to those who read this Post. 