I would want to read the application log for a time when the app is trying to load.
Ideally, I would "tail" the application log (<jira home>/log/atlassian-jira.log) in a terminal window, and then go to the browser, click "enable" to get the app to try to load and watch what happens in the log. I expect it to dump out the "errors that prevent it being enabled".
Those will probably be large blocks of inscrutable text, but the header lines are likely to contain decent pointers to the problem.
My guess is you have other apps with clashing libraries, but it could also be resource problems, memory, or simply that the app is not valid for your version of Jira or has a bug. The logs should help narrow down those possibilities.
I don't have the time to plough through a massive pile of someone else's logs, I have enough of my own (client's) systems to look after.
You don't need a lot though, as I said, start tailing the main log, provoke the error, you'll get a few hundred lines of text, most of which you can ignore, you're only interested in the headers at this point, the individual lines with numbers are for referring to code.
Catch up with Atlassian Product Managers in our 2020 Demo Den round-up! From Advanced Roadmaps to Code in Jira to Next-Gen Workflows, check out the videos below to help up-level your work in the new ...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events