Even if that clause is enforceable, you can just tell people about it instead. No company would try to prevent talk about their products' good performance.
Actually, I’m obviously not talking about Jira but imagine some made an issue tracker in cloud mode and programmed it using microservices, the speed of each microservice would vary a lot depending on workload, time of the day, location, time since last access of the document/attachment/screen/userdata, configuration of the instance, importance of this customer (maybe I would give privileged speed to a good customer, or to one whom I’ve had problems with on other features) and it would vary so much that performance for one person would be hardly representative of another person’s experience.
That would be one legit reason for thinking about writing this clause. Because it’s really curious to think about writing that.
Not that I disagree, although I feel the problem here is that this clause then can apply to all types of softwares. And even hardwares too. Just think if tomorrow Apple says that you cannot talk about degradation in performance in iPhones (because battery capacity reduces over time or something). We both know this, like we know that a user's experience will differ from the other. A company shouldn’t be adding a clause to prevent talking about this, it sounds like a malpractice to me. (I know it’s not that serious but still…)
That would be one legit reason for thinking about writing this clause. Because it’s really curious to think about writing that.