Broken links to Confluence pages are not visible in the new issue view. In the old issue view the error "wiki page failed to load" is displayed instead of the link.
1. Open an issue
2. Link a confluence page in old or new issue view
In the new issue view, sometimes the confluence links are not visible at all, some other times they show an error message like the one in below screenshot:
Sometimes this issue is caused by some leftover Application Links pointing to an old Confluence site and it is enough to remove those application links by following the steps in: How to Remove Application Links via REST API
However, in case this won't work, you may want to Contact Support in order to have this issue addressed.