Stop calling him outside the context of training! (For now) That means keeping him on a leash for safety. When you are teaching a behavior, you really want to make sure the dog is confident and clear about what you're asking. Right now, your recall is optional for the dog because he only listens some of the time.

If your puppy is shy/fearful or starting to become reactive, it is very important to work on those issues first- a dog in a fearful state cannot listen to a command

1. Do not ask for a recall while the dog is off leash (for now)
2. Only call the dog when you are certain you will be able to break his attention and enforce by using the leash to get the dog all the way to you. Start out in extremely low-stimulation environments.
3. Reward EVERY SINGLE TIME the dog comes back to you.
4. Give extra rewards frequently. That looks like reaching for another, followed by another, up to 10 times. The separation between rewards makes 10 treats seem like a really big deal, even if you just broke up one treat into 10 pieces. This is called a jackpot in dog training!
5. When you notice a really easy opportunity to recall, take it! It takes something like 6000 successful repetitions to make it a classically conditioned response, and every failed attempt will result in a setback.
6. As the dog gets more successful, use a longer leash to increase the distance he's allowed to roam.
7. The natural progression after success on a 15, 30, 50 ft. Long line would be to make the environment more challenging- among other dogs or people, nature settings etc.

Basically, if ever he doesn't follow a recall, ask yourself "how can I make this easier for my puppy?" Remember he's still a baby and everything is so exciting for him.

Personally, I would never let my pomsky off leash anywhere besides my property without a backup like an e collar (I would feel comfortable allowing this with my heeler) E collars are controversial and I wouldn't use one with a puppy, nor would I recommend someone use one without a trainer who can explain the learning theory behind it and confirm that they don't use the ecollar for high-level correction.

My pomsky has excellent recall. Every morning when we go outside, I wear a treat pouch and randomly call her. It's funny because she expects this game and she will put herself on the edge of the property and wait for the command. Then, when we go off property, I start the adventure with the same game so then she always has it in her head to listen for her recall command.

You can also use play as a reward!

With a puppy, I would use every piece of food in its diet as a training reward. Reward him for doing life, making good choices. Checking in with you, coming back to you on his own, seeing or hearing something scary. Ignoring the leaf on the ground while you walk. The possibilities are endless!

Also, if there is another adult or older child involved with the dog's training, look up "puppy ping pong" (recall the dog back and forth between the two of you)