As long as Atlassian is in the process of redesigning Jira issue View - Smart Checklist add-on might not work properly on Issue View pop-up.

Check the news here: https://confluence.atlassian.com/jiracorecloud/the-new-jira-issue-view-938040503.html

More extended info for add-on developers

https://developer.atlassian.com/blog/2017/12/alpha-program-for-the-new-jira-issue-view/

How to fix:

"The new experience is available for everyone using Jira Core boards, and we're incrementally rolling it out to Jira Software boards and backlogs. If the new issue view doesn't fit how you work in Jira Software right now, you can turn it off in your profile under Labs."

From our end, as the add-on creator, we will be following Atlassian recommendation and adapt add-on to the new issue view in coming months.