I have the same problem with the Samsung D980. Three days ago my touchscreen starts to freeze. I tried everything and a temporary solution is to shut down the telephone and remove the battery for half an hour. Then it works again, but after a while the touchscreen freezes again.
Although my touchscreen sometimes got some waterdrops on it, it don't think this caused tte problem. I think this is a software problem. When you disconnect the battery for half an hour untill an hour, the mobile phone maybe get a kind of a reset, because afterwards it works fine for some short time and then the touchscreens halters after receiving a phone call or pressing a lot of times on the screen.
This suggests a softwareproblem, which could be solved by new firmware, but I can't find it on the internet. Somebody any idea?