I use Youtrack at work and it suffers from being WAY too configurable, to the point that nobody uses it because you have to click SO MUCH to do anything.
Every developer we hire has to sit and watch 10mins of videos so they know how to use it, yet every other issue track I've used has been immediately obvious as to how it is used.
It does some really annoying things too, like hijack the history state of your browser, so pressing back and forward doesn't work as you'd expect (they have their own back button in the app, you're "supposed" to use that).