I had the same problem when I was building my Panther, I got it from one of the newer HL production batches and the stock springs were pre-clocked from the factory. With metal tracks on, the weight increased significantly and the stock pre-clocked springs couldn't elevate the hull once they were compressed. You could experiment and tighten the stock springs until the desired force is achieved, but I'm not sure if you want to install and remove 16 interleaved roadwheels and their suspension arms over and over again!

Personally I simply paid the 10 Euros and got some stronger Asiatam springs from Welshdragon.