Thanks for the patience. A fix for this bug has now been deployed and the fields for the Next-Gen projects should now be available again. We will now proceed with the closure of this bug. If any problem persists, please do not hesitate to reach out via https://support.atlassian.com.

Agree with Scott this is a major pain on my teams productivity - My project is rendered useless right now and I've moved to general verbal discussions in Slack about who should be doing what. I cannot assign any tasks to a user normally (nor can anyone on my team) and other form fields are just missing completely and inaccessible. 

The work around I've managed to work out today, which is NOT a long term solution by any means;

1. View the ticket in backlog view, move it to the board. 
2. Arrange the board by assignee swimlanes (there must be at least 1 ticket to your assignee already on the board for this to work)
3. Drag the ticket from the unassigned swimlane to the assignee's swimlane. 

Otherwise... Create the ticket in a different project, assign it to a user then move it into the next gen project??!!?? 

I'm not sure this level of basic project instability is worth it for the only major advantage of roadmap epic view right now    

Not really a workaround, but kind of: You can access all fields in the jira iOS app just fine.

I need a fix or workaround for desktop ASAP though as this renders a couple of our projects useless.

Is it a config in my account that's caused it? I've uninstalled recent plugins I've added and that doesn't seem to have solved the problem.