process sometimes does'nt work

hello,
i'm using CO for years. For the first time, with CO 9.0 there is a problem with process: sometimes, it does'nt work for variants. But if I process on the same time the original and the variant, it works for both. That problem doesn't occur always, only sometimes. So then I have to process the both, and then erase the original output processed..
W 10 64
Out of that, it runs very well, quick and without memory difficulty..
merry Xmas...
Lilo