Also there's bithumb.net but it's redirected to bithumb.com which means both domain are run by the same company. If someone could clarify and make it clear that the bithumb.pro is part of bithmub.com ... would be nice to remove the doubts here.
I think what MDZZ and joeycoin said is correct. It seems like both domains are owned by Bithumb. Bithumb.com deals with markets realted to South Korean currency while global i.e bithumb.pro deals with transaction related to USDT.
One is kinda like domestic trading platform while other is global platform.
It's better to get it cleared out with support but bithumb.pro also doesn't have any bad reports yet so they are doing legit business-
I guess