Comrade, I ran into the same problems as you.
First, sorry for my English.
Second, the solution is:
- Go to the settings in the main menu, check the item "advanced detail settings". (If you haven't already done so)
- While building in VAB, right-click on the falcon's legs, change the "spring/damper" settings.
- Try setting them to different values, my legs stop exploding when the spring is set to 0 and the damper to 0.2.