Standstill to me conveys the feeling of waiting to move again, where as halt seems like a definitive stop, without the thought of continuing.

A "halt" is more enduring. A "standstill" may be temporary. Think about the origin of the word "standstill". It comes from "standing still". Generally, when a person is standing still he starts to move again a while later.

I don’t think there is a difference. They are synonyms for each other.