OK Im going to assume that you control/drag shorter in order to speed the clip up.
You are saying that if you have multiple events (Sonys term for clips)on the same time line and you speed up an event and then close the gaps that shortening the event would create, that the timeline will not render correctly? (What are you rendering too?)(What type of file is on the timeline?) Can you post a screen grab of a timeline that won’t render?