Why does my dog eat from me but not my partner?

We have a 7 month old puppy who has been behaving strangely lately. We have had him for 5 months now and he used to take food from both my partner and myself. But this last month or so he refuses to take food from my partner. He has no problem with him otherwise. He plays with him, cuddles with him, goes on walks and does pretty much everything except take food from him. My partner has tried to be calmer around him and gentler with him but that hasn't helped much. He also tried giving lots of treats but sometimes our puppy refuses even treats from him although the next minute he would play with him. We are not sure what's going on and if we should just insist that he eats when my partner feeds him. Any advice would be appreciated!