Hi,
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
Sometimes this is happening that INACTIVE sessions (600+) are not getting cleared in V$SESSION even after many hours!
What I have observed more is this is happening when the server get overloaded with sessions..
There is no IDLE_TIME is set as of now, not sure if that can help as if client application does not acknowledge ...then session will be there with SNIPPED status.
Regards
Hesh