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I think it's largely due to the current huge demand from an incredible amount of new crypto enthusiasts. They mainly have scaling issues which is being resolved by adding new servers. Will take them a little while though...

If they are largest exchanging company, What do you think they have lazzy servers? Or may be employers are lazzy, because they are doing business of million dollars.

Doesn't really matter right. All that matters is that they are working on these scalability issues, hopefully they'll be back in business as soon as possible. The entire crypto sphere is extremely immature... will take a few more years until most of the entities will be running smoothly as you'd assume it should be.