Thank you so much! I've also found out myself just now it's the Mittlere Einheitswaffenträger and also known as the Krupp I (Egen) Waffenträger. Apparently a prototype was developed with a 10,5cm LefH, which was supposed to be interchangeable with a 12,8cm as seen in my original image and a 15cm sFH.
Attached are some photos of the prototype