1. Have you logged in your KC account with a new device or different ip recently? This includes using a vpn with the same device.
2. Are you trying to withdrawal an alt or niche coin? I consider alts anything not btc or eth.
3. Did you recently deposit a crypto currency and instantly sell it for usdt, then tried withdrawing? For example, depositing 5k worth of eth, then selling it on KC for usdt, then trying to move it to coinbase instantly.
These are the big three reasons I personally think people are getting their withdrawals blocked. With alt coins they are more prone to having network issues it seems like. If your withdrawal have been blocked outside of these three reasons, please share your experience.