I got an email from the exchange I use stating the Istanbul hard fork is to occur at block 9069000 at approximately 15:44:36 PST on December 7. It happened already but they have suspended all deposits and withdrawals from happening until further notice.
It is not a contentious fork and so does not result in any new coins from it happening.
So why would they decide to suspend all transactions of ethereum?
For that situation mate, we can't determine what reason it is but what certain for now is this will probably prevent more dumps of eth. I think this was a very serious preparation of the incoming bullrun if it won't fail in the long run. So let's see what it take in the future.