A few customers reported that cleaning Jira related local storage/cookies/logging in again the browser solved the problem.

Please contact us if the workaround doesn't work for you.

Other vendors are affected as well as this is a bug in Atlassian Connect Framework, the issue is tracked as https://ecosystem.atlassian.net/browse/ACJS-1134

A few customers reported that Jira instead of showing Clockwork pages displays an error message starting with "We're having trouble connecting to Clockwork..."