My thought might be he might not recognize you as the pack leader. Do you have him eat first before you? Maybe stop the free feeding. Only reason I say that because he is out of the stage of hypoglycemic shock as a puppy. There are ways to make sure your dog will not become the poster child for starving doggies when changing the feeding ways. (The previous comment was not by any means attacking those who do offer the free range of food eating. If you thought that it was I am sorry but it was not meant at all.)
Pick a certain times for it to be meal time. You can always reoffer the food 20 minutes later. If he knows any commands throughout the day you can use normal kibble or healthy treats. In between meals give him a carrot or banana smeared on a bone which was frozen. You can put some kibble ontop of the smeared banana. I call it dog ants on a log. Get it because of the ants on a log treat but using kibble instead of raisins.
. Make him work for it whether it is to sit or any other command he knows. Anything he gets from you he should do a command for it to earn it.
There is the thought of putting food into a treatball. Thus he rolls it and food comes out. Introduce it as fun game and maybe that might work for starters. We did that in the past for our male Biewer just something different for him during his meal time.
You tube can be a good help with learning how to do basic commands if he does not have any. Also, just searching on the web if you already have not. But I can guess you already have at this point.
This is not an hopeless case just will require lots of work and being consistent. That is the key being consistent. Also be or pretend to be excited in giving him the food. These are just suggestions. I am no expert on dogs I just have been learning with them for about 6 months. I have been though like many reading and learning from others especially from here. My wife though has been training and working with dogs since she was 5 years old. I learn from her as well.