"The line 'DefaultLine 21' needs to be connected to an Activity" error appears:
This is caused by orphaned values in the HTML5 json schema. To test this, please run the following SQL script:
USE [K2] --todo:Change to K2 DB name
SELECT [P].[Name], [P].[JsonId], [C].[Id], [C].[SessionId] FROM [Designer].[Process] AS [P]
INNER JOIN [Designer].[CollabData] AS [C]
ON [P].[JsonId] = [C].[SessionId]
WHERE [P].[Name] = 'Test\Test' --todo:Change to workflow full name
AND [C].[SessionId] = [C].[Id]
If you deployed recently, and made very minimal changes (or no changes), open K2 Designer and navigate to your workflow.
Click on "Delete" and select YES on the confirmation:
Note: The icon of the workflow will change after the delete:
Edit the workflow using the K2 Designer and deploy again.