After update from 5.7.1 to 5.9.4 no direct creation of Jira issues is possible - why?

[M.Evans]

When highlighting text in a Confluence page and choosing the "Create JIRA issue" option, we get this message:

The version of selected JIRA server is not supported. You may want to upgrade to the newer version or create issue in JIRA.

Our JIRA has version 7.1.1

If you choose : create issue in JIRA, JIRA is opened after a long while but only displaying the dashboard. No new issues is created.

[M.Evans]

[CSP-182781]

Flush plugin cache:

https://confluence.atlassian.com/confkb/how-to-clear-confluence-plugins-cache-297664846.html