Medical.
I went through screening of KAL about 2 years ago for B737 DEC position. I passed all the tests, simulator, interview, etc. but failed due to medical. I didn't get any detailed explanation except I don't meet their medical standards and it was not something that can be corrected. I passed 2 medicals in my own country two times without a problem after that. I have to use supplementary medicine since the removal of my half-thyroid about 4 years ego and in my last medical the doctor saw something suspicious with my heart activity and did detailed testing which turned out to be OK at the end. After couple of trials I finally got information from KAL that it was my heart condition and hormone levels (due to thyroid removal I think) that didn't match their standards. So, I agree, their standards are higher than normally required.