Hi Dovlet,
I simulated this, as in the attached file, and it did not happen that the balls sank in the sand. You just have to change the “restore shape” value in the “object” tab to 0% and slightly raise the “size” and “step” values in the “advanced” tab. I saw that you are using “clothe surface”. If you do not need it, you can delete it, as it may be the cause of the problem.
I think that it is better to open a new topic when you have another subject to make it easier later for forum visitors to benefit from it through the search feature.
I hope this helps you.
Thanks!