Hello and welcome to the forum. How much food are you giving your dog? Are you weighing it? For an active adult dog you need to be giving 1.2% of the ideal body weight.. Having lost 0.7kg you need to add that on when calculating the amount. I fed this type of food for some time but it was the ones made by Markus Muhle and at that time Cobbydog had not started making it. The fat content is not very much higher so I am not sure whether it would make much difference.
As you are using Markus Muhle food you can contact Beate Rothon of Gentle Dog Foods for advice if you wish. Her contact details are on the Gentle website or you can post on their Facebook page.
First of all make certain you are feeding the correct amount. Secondly, it might help if you hike up the protein/fat content by providing a topper once a day. Fresh, home cooked foods would meet this criteria eg minced beef, lamb, sardines, chicken, turkey. The first two have higher fat levels. This would also add variety. As mentioned in my last post, if you want to know more about adding homemade food as a topper, check out the YouTube videos made by Rodney Habib.
Edit: You didn’t say how much exercise your dog has. In the past we had a poster who was giving their dog an awful lot of exercise - several miles a day IIRC. It was not surprising that the dog was failing to gain weight. If you feel that this might be the case it might be worth lowering the exercise for a little while. Dogs need to be calm but it’s something that might need to be taught. Using their sensory organs eg smell is also good exercise.