Here's a couple of ideas-First, make darn sure you have the track properly connected-it's real easy to connect the track and have the rail ride on top of the connector rather than be seated inside. The change in rail height can move the couplers up and down enough to let them come apart. Second, using your coupler gauge, make sure that the couplers are set at the proper height. Last, using a flashlight, watch closely and see if your "brake lines" are somehow twisted and hitting each other on the curves. If they clash, they can force the couplers apart. Bend them in such a way that they don't foul each other. After that, I'm at a loss. Best of luck to you.
John Tumolo Britcarfan@aol.com
John Tumolo Britcarfan@aol.com