Hi @Reynnoldsnumber,
Yup I do think you identified the problem correctly in that the material point is causing the problem. The material point is intersecting with your geometry causing it to “disappear” so simply moving the material point and ensuring it is not intersecting with any geometry but is within the simulation domain should solve your issue.
With regards to what the material point is you can refer to my earlier post here.
Cheers.
Regards,
Barry