Forge app's post function not getting triggered from Issue Workflow

We have a customer (on Jira Cloud) for whom our Forge app’s post function is not getting triggered when their issue is transitioned. This used to work fine a week ago but stopped working now.

We have confirmed that the post function is setup on the right workflow by using the out of box “set assignee” post function. The assignee does get set correctly. We have also tried setting our app’s post function on both create and done transitions. And neither transition triggers the post function. We have confirmed that the app post function works in the customer’s sandbox instance.

We believe this is something to do with how Atlassian Forge triggers our app’s post function. However we are unable to debug further as that handoff is a black box, with no logs available.

Any suggestions much appreciated.