The mistake that many westerners make is forgetting that different cultures put different emphasis on different values, and this has been the bane of international business for a long time, and now as the world is getting smaller, individual teams are facing the same issues.
In Korean and Japanese culture, bringing up potentially embarrassing things publicly can be very awkward, there is a great amount of shame in feeling that you have failed, or lost face, or caused another to lose face. To point out another's errors is to cause that person to lose face. To point out one's own is publicly losing face. To disappoint the boss is to lose face. Worse, to point out the mistakes of the team could make the boss lose face.
The best way to address this with your team members who are not raising issues is to tell them that it is not only okay to do so, but that it is necessary. Ask them if it saying so in public that is the issue. Find out what the obstacle is, and take action to correct the problem. If you assure them that there is no shame and embarrassment in discussing these things, or better yet, that you want to make sure that the team itself will not be embarrassed, that may help you. This could be VERY effective if you put it this way. "Your feedback and input protects the team, and myself from embarrassment, you will be helping all of us by bringing things up sooner, when they may be addressed quickly, with help from the entire team. But in any event, you need to change your approach
If it means discussing things privately, do so. If it means acclimating them to the culture, do so. If it means following up with them individually, do so.
What is certain, however is that if you take the same action, you will get the same results.