It is intereresting this past weekend REX was in Africa, and cancelled his visits in Kenya due to illness, then cut his trip short to go home.
He was upset that he was out of the loop on the SK/NK thing. He was caught off guard by reporters in Africa, and flew home.
The same day that SK read the NK invitation at the White House Tillerson had given an interview in Africa saying negotiations with NK were out of the question.
Sauce: CNN, AP, etc. Easy to find and covered heavily.
We were busy connecting Kenya and didn't read much into the fact that Rex didn't have a clue that NK was going to invite Trump.
Sec. of State clueless