What problem you are facing on that exchange it has big volume so you have to give us more details. This exchange is supporting Mainnet token so that people are moving towards this platform so if you found something suspicious than share with us.
"The withdrawal operation needs to be verified"
there are no limits without verification
and
"Dear user：
Your verification has not been approved, please go to the website to check the reason"
For Bitrex okay this is not like
Some exchanges made it mandatory to complete the KYC before making a withdrawal. Try contacting UEX's support if you think there was an error with your verification