I am experimenting with latest hub and youtrack on a linux machine, I installed latest versions (2019.2 and 2019.1 respectively) and enabled the hub integration in youtrack. (not using https for the moment, old plain http is used)
What happened is this:
This happens as well with older versions (2018.4) of hub and youtrack.
As far as I recall this is bug in Hub yet to be fixed.
2-3. There's known issue with that: https://youtrack.jetbrains.com/issue/JPS-9928