Sometimes problems can arise when you have poor volume representation for some parts of your model. To see the volume representation for each part, turn on the Show Collision Guide Geometry on your RBD Object. You can also changing the viewport’s visualization to Wireframe mode to better see your geometry.
There are two ways of of handling problem parts. The first way is to improve the volume representation, and the second way is to use a thin shell representation.
For the volume based approach, the geometry should only contain closed surfaces. You can also improve the output by remodeling the objects to be thicker or by increasing the number of volume divisions.
The second solution is to treat the parts as thin shells by turning off Use Volume Based Collision Detection. If you make this change, you should also explicitly provide a mass for the object (turn off Compute Mass) since DOPs will be unable to compute a meaningful mass value from the density now that the volume is basically zero.
Generally, you should create closed surfaces for the geometry when objects are thick. You can use open surfaces and have DOPs treat them as thin shells when objects are thin.