How to troubleshoot enq: TX - row lock contention?
Query v$transaction on each node to see uncommitted sessions:

SELECT t.start_time, s.sid, s.serial#, s.username, s.status,s.schemaname, s.osuser
   , s.process, s.machine, s.terminal, s.program, s.module
   , to_char(s.logon_time,'DD/MON/YY HH24:MI:SS') logon_time
FROM v$transaction t, v$session s
WHERE s.saddr = t.ses_addr
ORDER BY start_time;