Summary

If a workflow has a broken transition or missing element, no error is displayed as such in the UI. Transitions will not be available on the issues, but there is no indication as to why. 

Reproduction Steps

In this scenario, a workflow is imported to Cloud utilizing REST API. 

/rest/api/3/workflow/update 

If a workflow is imported from one Jira site to another, the internal ID's for those workflows will inherently change from one site to the other. This can cause some transitions to not have assigned screens, as there is no matching ID for that value. 

As this workflow has a NULL screen, all transitions in the project are unavailable. 

Expected Results

When this scenario occurs it would be expected to see a more pointed exception in UI that points more directly to the source of the issue. 

Actual Results

The information shown is vague and does not provide a pointed "error" message to the user. 

You have to dig into dev tools and search for the correct 500 error condition to source the actual error. 

Workaround

Currently the workaround for this behavior is to source the error in console logs and manually update the project workflow. In this case editing and assigning a screen to the NULL value.