Initial direct transfer and security mode establishment failure Solution

CORE
,
#1

Hello Experts.

I have following issue:

Release Cause
Normal
Initial direct transfer and security mode establishment failure

If Radio condition perfectly fine, then it should be at Core end issue?

#2

Initial direct transfer and security mode establishment failure Solution
Initial direct transfer and security mode establishment failure Solution807×400 92.8 KB

#3

But here is cause value 15 → IU release command.

cause value 15 -> IU release command