I was voted the best answer on a post - and I was the only one posting. The question was then downvoted and I no longer have the reputation from being the best answer. Is this related? Or did the OP decide he didn't like my answer. Thanks.
The green checkmark is solely assigned by the original question poster, and has no relation to voting - either on that answer, on the question, or anywhere else. The original poster may at any time assign, change, or revoke the green checkmark at his/her discretion.