User sometimes receives "Action is completed" although there is activity chaining between 2 tasks

We have a process model and it contains some scripts and another subprocess between two user tasks all nodes are connected by activity chaining, User sometimes receives "Action is completed" although there is activity chaining and by analysis this happens when the subprocess takes time so by search we found that we have to increase conf.suite.REQUEST_TIMEOUT_IN_SEC in custom.properties so we increased it to 180 but still this behavior happens and the subprocess takes 28 seconds