Next-gen issue is not shown in Sprint section in Classic board

Issue Summary

When Next-gen issue is dragged from Backlog to Sprint section (Classic board), it will stay in Backlog section after page refresh (it only affects for Kanban next-gen project type).

Steps to Reproduce

1. Have 2 projects; Classic Scrum type and Kanban next-gen project type.
2. Create some issues in both projects
3. Create a filter that include both projects
4. Create a new board based on the above filter
5. Go to the above board (Classic project) > Create a Sprint
6. Move some issues from both projects to the Sprint
7. Start the Sprint > Refresh the page

Actual Results

Issues from Kanban next-gen project type are not grouped in Sprint section (they stay in Backlog)

Expected Results

Issues from Kanban next-gen project type are grouped in Sprint section

Notes

• Those issues from Kanban next-gen project are still shown in Sprint Report
• Searching in Issue Navigator (Sprint = <Sprint ID>) doesn't return issues from next-gen project
• Issue history recorded that the issues from Kanban next-gen project are correctly added in the Sprint

Workaround

• Go to Kanban next-gen project configuration
  • https://<URL>.atlassian.net/projects/<project key>/settings/features
• Enable both Backlog and Sprint
• Disable them again