There could be a few different reasons why your window isn't able to close properly. The first and most common issue is that either the operator or one of the hinges aren't working properly.
An easy way to verify which part is causing the problem is to first disconnect your operator from the sash and then close the window by hand. If the problem persists, then you can rule out the operator as the culprit. In that situation the hinges likely need to be replaced.
If the problem is fixed, then you know that the operator is the source. Then that would have to be replaced, instead.
I would try that experiment out first and get back to me. I can advise accordingly.
