Prepare install task instance is stated two time when i complete "Request engineered d..." task and again started when i complete "Prepare BOM RDBMS......" task.
i want this task should be started one time only from either point.
It is hard to tell from your description of the problem, but it sounds like you are transitioning to all of the flows leading from "Request Engineered" rather than including logic in your process that selects only one transition.
Alternatively, you could have a single transition out of Request Engineered that leads to an Exclusive Or gateway. That gateway can then make the decision about where to transition next.
I recommend that you create a small example process that illustrates your problem in a simple way. Perhaps create a project using the all-in-one archetype and put it on GitHub so that we can actually look at the process and provide assistance. Processes can be complex, so screenshots are probably not going to be sufficient.
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