Symptoms
Can't open workflows through the K2 Designer
Diagnoses
Can't open workflows through the K2 Designer. HTTP 404 error when attempting to edit a workflow.
Resolution
Authentication for Designer and Runtime site had been changed to using Windows Authentication after the database consolidation, as it was prompting for which authentication method should be used. As such, we set AzureAD Issuer's "Use for For Login" = false (via System > Management > Security > Forms > Manage Issuers) and re-enabled Forms Authentication to achieve the previously configured behavior prior to database consolidation.
