Database Software

Hi all, Yesterday we observed that for no apparent reason, one instance in a RAC database appeared to be left out of the listener load balancing equation. This resulted in a very high load on the remaining instances. The only way we could repair this was to restart the un(der)utilized instance.
Before restart:
SQL> select count(*),inst_id from gv$session group by inst_id;

COUNT(*) INST_ID
---------- ----------
216 7
41 12
220 9

After restart:
SQL> select count(*),inst_id from gv$session group by inst_id;

COUNT(*) INST_ID
---------- ----------
222 7
218 12
224 9



Has anyone else seen this? Is there any way to tell what is going on? Is there any way to fix this without restarting the instance? We have tried restarting various listeners without success. Thanks in advance, Mike