It doesn’t sound properly fitted. That doesn’t mean just tighten it so he can’t get it off, that means have the nose band high enough he can’t, (short nosed dogs need different head collar)
The cooler for our lab was too long at the sides so I just sewed it 1/2 inch shorter each side and now he can’t get it off.
Also if you make a big deal when they are wearing the head collar, praise them lavishly and pet them, food treats help when your putting it on at first, make it someth8ng special always, never loose your temper, dogs serve that and try all the harder to get it off.
I call my dogs, tell them time to get dressed and make a big fuss over whomever I’m taking out. They all get a peanut sized piece of dried chicken and then praised hoe big they are and hoe good they are. They will Stand and park out, raise their heads for the head collar then prance all the way to the door excited to be going out and about.
To speed up the training process we do several indoor practices of treat, reward, wear and then take off in anywhere between five to ten minutes. As soon as my guys hear get dressed they are ready and waiting vs running and fighting like they used to.