How to trace whether application is flooding listener or not ?????

Hi, when I am directing applications on listener-1, it becomes very slow and applications cannot get connection. But at the same time I can get connection to DB using listener-2 from the same application server. Now if I direct applications to listener-2, listener-1 becomes normal and listener-2 stops working. If this is happening for application problem, How to confirm it from database side?

[everything was working fine before some days and I never changed anything on DB, also except some testing no operation is going on to this database]

DB Alert log:

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Fatal NI connect error 12547, connecting to:

(LOCAL=NO)