I am having an intermittent problem with the right wide curved switch. Some coaches, a silver liner, and a red double deck Regio car have problems on the switch.
It can happen in either direction. The red Regio control car lifts, but does not derail. I think it is the pickup shoe lifting on the frog. The silver liner it is the middle coach lifting at the frog and derailing. This is in push mode, not. A problem in pull.
Do i have a defective switch? This has not been a problem on the tighter curved switches, or on strait switches.

D

First thing to check is to observe whether the buffers of any of the coaches are impinging on the buffers of adjacent coaches.
You should also check to see whether a coupler is contacting the buffer of an adjacent coach.

The next thing you should check is whether the problem occurs in the same spot if you rotate one or more of the coaches by 180 degrees.

Is the Silberlinge (Silver Liner) a normal coach or a control coach (cab)?
The Red Doubledeck Regio coach is a pilot coach. Is the slider at the lead (cab) end or at the other end?
The slider exerts downward pressure. As it passes over the raised studs of the switch track, this can cause the bogie to be lifted off the rails.
In some cases, placing additional weights over the slider bogie can reduce this problem.
You should also check to see whether the slider is impinging on the coupler shaft. If this is the case, you may need to use a shorter or offset slider

Most Märklin coaches since the late-1970s have had had adjustable buffers.
It is rare that Märklin coaches have issues with their own close couplers, but if you find the coupler to be an issue, you can either try swapping one out for a regular coupler or use a different coupling that may work better with the buffers.
Coupler and buffer issues may not occur in regular curves, but may occur on switches and on S-curves depending on the track setup.

Regards

Mike C