First, I would check whether all the required Appian objects and dependencies, including the third-party plugin, have been deployed correctly to the QA environment.

Once I verify the deployment, I would test the same functionality using my own account in QA. If it works with my account but fails when the QA user runs it, I would compare the permissions of both users.

In Appian, the important point here is that the third-party plugin node requires the user executing it to have System Administrator privileges. Developers may have System Administrator access in the Dev environment, while the QA test users may only have Basic User access.

So, if the process model or plugin node is configured to "Run as whoever started the process," the plugin will execute using the permissions of the QA user who started the process. Since that user only has Basic User privileges, the plugin fails.

To fix this, depending on the security requirements, I would check the node's Run As setting. If appropriate, I would change it from "Run as whoever started the process" to "Run as whoever designed this process model." Then the node executes using the designer's System Administrator privileges rather than the end user's permissions.

I would also verify the deployment account. For deployments to higher environments, I would use the organization's standard deployment/service administrator account rather than an individual developer's account. This avoids issues if a developer's account is disabled, removed, or doesn't exist in the target environment.

So in this particular scenario, if deployment and configuration are correct, the likely root cause is the QA user has Basic User access while the some third-party Excel plugin requires System Administrator privileges to execute.