SM customers no longer able to schedule issues via the "Due date" field when not on portal.

[Sara Innes]

Hi there - I'm the owner of my company's long-standing Atlassian environment. There is an SM project within this environment that has a user portal set up, but has historically had users fill their tickets on the back-end of Jira. This has worked for a long time and no real changes have been made to their fields or permission schemes. 

However recently users attempting to fill the form on the back end have been getting a permissions error in regards to the Due Date field:

Field 'duedate' cannot be set. It is not on the appropriate screen, or unknown. 

After some looking, I figured that this must be an issue with the Schedule Issues permission and have attempted to amend it in a few ways to no avail. Attempting to grant this permission to the role Service Desk Customers yields an error stating that the permission cannot be granted to that group. Attempting to grant this permission to our Users role results in an error that JSM overrides the permission. I even tried "any logged in user", but again, overridden. Users have zero issues logging through the portal, as the "Service Project Customer - Portal Access" permission group works. 

As a workaround, I can use another date field that users fill that then clones into the duedate field via automation afterward, but would rather know if there is some way to address this for the team using the project first. 

Did something change regarding scheduling issues in JSM recently? Am I overlooking something?