Order was filled, but could not find position

I had an stop buy order that was shown on the platform(C2 web broker) as “filled”, and this position also showed up in trade record page. But when I want to sell it, could not find my position on the platform. And when I tried to sell the same amount without clicking “close”, I got a message" you can not sell because you do not have position".
A couple of munites later, my position show up and I sold it, at 3 points lower than the price when I first tried to sell it.