we solved the issue with defining a log card interface.Although defining that port was mandatory for 8.1 regarding to Admin guide , it was working fine without that interface.Management interface can forward logs without this port at 8.1 and this was an internal bug , paloalto Tac confirmed.
Also if you define only subinterface as log card with ip ,it also fails.So an ip(it can be fake) should be given to log card main interface directly and then subinterface with ip works.
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