Unfortunately, support does not always respond in a timely manner
hopefully we can help you a little bit...
1. Sometimes this happens to me too during big gem sales. I don't get a black screen, but nothing happens when I tap on the gem counter or any "buy" buttons. Restarting my device usually does the trick. I don't know if you tried this but if not it might help you next time.
2. Gem promotions are offered to some people and not others. Some users get offers for free itmes with gem purchase, or certain sale prices, while others may get a different sale percentage or none at all. I would like to see this changed, but unfortunately for now that's how it's working.
3. I've experienced this too, but never gotten an answer about it. Sometimes my missing XP returns and sometimes it doesn't. Maybe someone else can help you here