Steps to replicate

1. Make a copy of the default jira workflow
2. Place a new status on the graph
3. Draw a transition from In Progress to the new state
4. Choose Clone Transition
5. Clicking "OK" on the previous screen
6. Press the ESC key on the keyboard from the previous screen - notice that the transition arrow disappears
7. Delete the added step
8. Exception will be shown. Does not appear on the logs.

Kindly refer to the screenshots attached.