I think some others are having problems with the witdrawal of RPX from Kucoin, it's a bit odd that it's only RPX that has this problem. It could be an exchange wallet problem and maybe posting on the RPX twitter or send them an email, rpx@red-pulse.com, or contact them on Slack might get things moving.
If you just want to withdraw your RPX for security resons then here should be no problem holding them on Kucoin, it's safe enough.