This is for the cloud-hosted versions of JIRA/Confluence, which do not allow changes in the application link between JIRA and Confluence.
When selecting text and hovering over, a pop-up normally appears to create inline comments, or open a JIRA issue. The Open JIRA Issue button is no longer showing.
Application links are there, no recent permissions changes, and all 11 plugin modules are enabled.
Possibly related issue, when attempting to make a JIRA Status Report in Confluence, it gives me an Upgrade your JIRA to 6.1 error. Could this be just an Atlassian hosting error?
And yes, this is similar to the following issue, which remains unresolved: https://community.atlassian.com/t5/Confluence-questions/Unable-to-create-jira-issue-from-confluence/qaq-p/625309