Summary
This issue occurs because due to a Jira update released by Atlassian that prevents a key Atlassian component from being used by JEMH 3.3.94 and below. In this scenario JEMH will install but cannot be enabled. This was originally fixed for Jira 8.22.3 however, this issue was back ported into Jira 8.13.21 and now requires an upgrade to JEMH 3.3.95 or above.
Solution
A fix has been implemented in JEMH 3.3.95 which will resolve this issue in Jira 8.13.21 and above. JEMH can be upgraded through the ‘Manage Apps’ screen at:
Jira > Administration > Manage Apps > Manage apps