Help very much required.

For the passed 2 weeks almost every day I seem to be having trouble with my car. I have a 2017 ford fiesta zetec 1.0 ecoboost. Sometimes when I am stopped in traffic then go to pull off, as I find the biting point and release the emegency brake the car does not move, even when I apply the accelerator. When I then go to reapply the emergency brake it feels very stiff and won't depress. If I try to move off again it does the same thing. I have to aggressively push the brake a few times to get it to unstick. This has happened a few times specifically when I have released the clutch a bit too fast and twice after the car has been stalled (when it doesn't' ask for a manual restart) but other times it just happens when it's a normal pull off. It is important to say that once the emergency brake has been released in these situations the car does not roll forward or back.

I've checked the brake servo to see if something was wrong with that, my brakes aren't spongy and usually just applying the lightest bit of pressure stops the car so I am not sure what is going on. My clutch seems to work fine too, my auto start stop works and I have to push the clutch down to start my engine, I also have no problem with changing gears (beyond the odd occasion where it pops out of reverse but this happened in my instructors car too which is the same model as mine) have tried to Google it but nothing that sounds like this pops up. I would prefer to know what it may be before taking it to the garage.

If anyone could please help me with this I would very mich appreciate it!

Is this not the "hill start assist"? Mine does something similar whenever I've stopped in traffic. I never use the handbrake (except when I'm actually parked up), but had noticed a "drag" sometimes when setting off after an auto-stop in traffic. I suspected it was the hill start thing so switched it off in the vehicle settings menu and the  drag went away. I've since switched it back on and modified my "setting off" driving style. 

If it is the hill start you just have to drive off not bother about flicking any switch it will release automatically usually quite smooth but now and then  will bind but only slightly before it goes off. Yes with mine I called the AA when I couldn't get mine to go off on my mothers steep drive all I needed to do was drive away with confidence . Don't mess with the switch as that is what confuses it .ITs the same with other well known cars makes to.