Hi
Oracle listener was by default set by SAP to listen on port 1527 instead of Oracle default 1521.
This is not true in the latest SAP versions.
Have you checked if you've got any network related warning/error in Oracle & listener alert log ?
Any message in SAP system log or work process trace ?
If not this it might be a network only problem (wrong config, defective element...) that is not related to SAP or Oracle => SCN would not be the best place to get help...
You could try basic diagnostic with tnsping from AS to DB to see if the roundtrip time does vary a lot
tnsping <Ora_sid / service> <number_of_times>
tnsping PRD 20
Hope this can help.