my DD was exactly the same. It was like she didn't know she could walk by herself, even when she clearly could and would 'accidentally' do it from time to time
DD was just like this, one day we were at playgroup and she just took off after an older boy (sign of things to come perhaps?) and that was it.... she just got it, and after that she was walking everywhere. I think she just needed to be distracted from trying to do it, if that makes sense - it's like she was overthinking it, and not believing she could do it, and when she forgot to think about it, she just walked.