Sometimes invalid arrow can be added to the map which is not visible.
This arrow can be hidden in the Activity background or backside of another arrow.
If we move the activity then also we are not able to find this hidden arrow.

Production And Test Environment

To resolve this issue, find out where the hidden arrow is present and delete it by following the below steps-
1. If you move the activity from its original location to the left or right and click on the save button, you will see the error for the activity where this arrow is attached.
2. Copy this activity and paste it onto the same map level
3. Delete the affected original activity
4. Click on Save and Done
5. The hidden arrow will be displayed in the red colour click on the edit Diagram button and delete the arrow.
6. Move the activity backup we made in the 2nd step on the original activity's location

When you face the error 'Save error Failed to save the current diagram' while saving the map diagram in a web client can be resolved using this article

"Save Error"
"Failed to save the current diagram"
"Web client"