Intermittent ORA-12516 ( TNS:listener could not find available handler with matching protocol stack)

JDBC Connections to my 11.2.0.4 Database are getting this error quite intermittently:

TNS-12516: TNS:listener could not find available handler with matching protocol stack

 I am asking you because I researched quite a lot about this error, and all solutions say this is a number of processes/sessions, but this is not the case, since sessions/processes number is quite low, and far from the maximum.

I searched in the listener.log, and only found "Warning: Subscription For Node Down Event Still Pending" warnings, and solved them setting SUBSCRIBE_FOR_NODE_DOWN_EVENT=OFF, but it had nothing to do with the error, because it keeps showing up.

Couldn't find any more information on the listener.log, only the same errors JDBC connections are getting (TNS-12516: TNS:listener could not find available handler with matching protocol stack)

Any ideas?

Thanks a lot.

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