are you using same name for both variables ? If yes, then its looks like you are facing issue which is reported in Bug 1152826 – Process Designer's Data Assignments editor overwrite existing data assignment when we try to add new data …
You are right!
I changed my assignments by using a new variable named prosessSuccess but still have the same problem. I still have a variable named success, but It is very hard to delete it since it is used in many gateways.