Active sessions with not null lockwait

Hello,

I'm working on a 12.1.0.2 two nodes RAC and I'm investigating a problem about 15 sessions of the same server that have a not null lockwait for a long time but the alert file doesn't include error message about this issue.

I ran the following requests:

select INST_ID,SID,SERIAL#,USERNAME,LOCKWAIT,STATE,STATUS,SCHEMANAME,OSUSER,MACHINE,PROGRAM,

to_char(LOGON_TIME,'DD/MM/YYYY HH24:MI:SS') "logon_time",

LAST_CALL_ET,EVENT

from gv$session

where lockwait is not null;

INST_ID   SID SERIAL# USERNAME             LOCKWAIT STATE               STATUS     SCHEMANAME                     OSUSER               MACHINE                    PROGRAM                     logon_time           LAST_CALL_ET EVENT