When you click on Test -> "Search Test Executions" on the left side a menu appears. But screen is greyed out and in the middle the sand glass icon is running all the time. You waited >10min - no change.Interestingly it might work fine in some other browser or in some other machine
1.Clear the browser cache and cookies
2.Perform a re index of both Jira and Zephyr for Jira.
3.If the above steps don't work check if the "block third party-cookies" option in the browser (here Chrome ) is opted.
If so add [*.]prod-play.zephyr4jiracloud.com to whitelist and now everything should work fine.