High change mass Explicit analysis

Hi to all

I have a problem with changing mass in an explicit analysis.

If I run the analysis which is made of 3 parts I get a change mass of 500%.

When I remove 1 part from assembly I get a change mass of 7%.

the 10 most critical element are not take part of part I removed. 
​​​​​​​The part I removed is in contact with another part and I tried all contact property  (contact pair, general contact ...) because I thought the problem was the contact between parts.

Could someone give me suggestions?

thanks 

Abaqus