Hope you have loads of patience, Vymuras tend to be very late maturing. Most dogs continue pulling once you have taken the Halti off, as the owners don't bother to train them as the Halti does the work. If you want to stop it pulling then you need to keep working at it, and gradually lessen the 'hold' you have on the lead, encouraging the dog not to pull as you would with a training collar. Titbits and vocal encouragement (watch me, good boy). I have used the Canny Collar and find them better than the Halti as the pressure is applied evenly to both sides as it crosses at the back of the head, rather than pulling up the side of the face.
Is your Vyleda unpredictable with other dogs? I used to work with one and she would be great with 19 dogs and suddenly shoot out at the twentieth for no good reason, and get back to you before you realised she had done it. No particular breed or colour, just when she thought you had
lost concentration!