I'm on the same boat and I was also considering opening a thread here, but so far reports of this happening aren't all that widespread.

The difference is I've had my account for years, used them successfully in the past, always had 2FA and never had an email regarding any unauthorized login attempt. So I have no clue regarding what's happening.

The worst part of this is that now I can't even withdraw my funds, so they've basically taken my funds as a hostage... Let's see how this plays out.

PS: I've successfully managed to withdraw from falling exchanges in the past... So something's definitely wrong on Bittrex.

EDIT: other users with the same issue in recent times on the following threads:
https://bitcointalk.org/index.php?topic=1663636.0
https://bitcointalk.org/index.php?topic=1957588.0
https://bitcointalk.org/index.php?topic=2053629.0
https://bitcointalk.org/index.php?topic=1954598.0
https://bitcointalk.org/index.php?topic=2038169.0

Their thread on the forums can be found here