Flow

Hello all, I am using SCCM since 1 year from now. And I got an issue on the computer association. When I use a *.CSV file to add computer to my collection which is containing 10 computers, sometimes I get only 6 computers to my collection (I have done Update collection membership), but the others 4 computers are not in this collection. I can find them in the collection All System and I have to move them to the good collection. Did you allready have this issue? Thanks in advance.