Alert log having KILL SESSION SOFT message in Oracle 12c

Message:

2020-02-24T13:40:15.733337-08:00
KILL SESSION for sid=(89, 18959):
Reason = alter system kill session
Mode = KILL SOFT -/-/-
Requestor = PMON (orapid = 117, ospid = 4628, inst = 1)
Owner = Process: USER (orapid = 112, ospid = 2308)
Result = ORA-0
2020-02-24T13:40:57.584304-08:00
KILL SESSION for sid=(283, 2650):
Reason = alter system kill session
Mode = KILL SOFT -/-/-
Requestor = PMON (orapid = 132, ospid = 1180, inst = 1)
Owner = Process: USER (orapid = 119, ospid = 7324)
Result = ORA-0


Solution
It work with idle timeout for the session and PMON process is cleaning the session according to idle timeout session and write message in alert log file.
You can ignore this message.

You can see its mode is KILL SOFT — mean PMON is cleaning the session. If its KILL HARD then someone manually kill the session in Oracle 12c.