Oracle session and process increasing - oracle

Question

so I have oracle 12c installed in cantos, the RAM 96GB and the disk are SSD which is pretty fast, and also an application is running on the same server with a lot of conversion and processing of the data.
this was pretty much new system that I installed database and application on it, so after couple of hours I see it give error of
"got minus one from a read call"
after digging around I see it was the session and process causing it so in increase that, but still after 24 hours I see the processes and session increasing it does not decrease when checking... bellow is the snap shot of the query during couple of hours I did.
select program,username,status,schemaname,count(*) from v$session
group by username,status,osuser,schemaname,program
order by count(*) desc,status
fetch first 3 rows only
2:00 PM 11 December
JDBC Thin Client oracleuser INACTIVE schemeName 233
SQL Developer SYS INACTIVE SYS 4
JDBC Thin Client oracleuser ACTIVE schemeName 3
select * from v$resource_limit where resource_name in ('processes','sessions');
6:55 PM 11 December
processes 490 492 1200 1200 0
sessions 500 504 1920 1920 0
After I observe it that it keep increasing I changed the idle_time in user profile to be 30 minute
IDLE_TIME 30
CONNECT_TIME UNLIMITED
after that I observe them for couple of more hours and run same query above and here is the results respectively.
8:25 PM 11 December
JDBC Thin Client oracleUser KILLED schemename 683
JDBC Thin Client oracleuser INACTIVE
schemeName 241
SQL Developer SYS INACTIVE SYS 4
8:25 AM 12 December
processes 995 998 1200 1200 0
sessions 1003 1007 1920 1920 0
NOW I see killed session and less inactive session, but they number of session keep increasing it does not drop I was expecting that changing idle_time in profile will kill inactive session and release the session and processes.
my concern is that when the session and processes hit the limit I set, I will getting again the same minus one error . and it will kill application also.
"got minus one from a read call"
any help will be highly appreciated
regards