ORA-04031 after upgrade to oracle 12c

Hi experts,

After I upgraded my system Oracle 11g to Oracle 12c I have the error ORA-04031 every week,

Errors in file I:\ORACLE\PRO\SAPTRACE\diag\rdbms\pro\pro\trace\pro_arc2_8028.trc  (incident=530484):

ORA-04031: unable to allocate 352 bytes of shared memory ("shared pool","unknown object","sga heap(3,0)","krsdicle")

Errors in file I:\ORACLE\PRO\SAPTRACE\diag\rdbms\pro\pro\trace\pro_arc0_14736.trc  (incident=514716):

ORA-04031: unable to allocate  bytes of shared memory ("","","","")

I have to stop the database and started again... I increase the parameter shared_pool_size but only work one-two days more...

What could be the problem? I have a server with 64GB and the parameters are:

_enable_shared_pool_durations        boolean     FALSE

shared_pool_reserved_size            big integer 405600K

shared_pool_size                     big integer 5G

sga_max_size                         big integer 32G

sga_target                           big integer 0

memory_target                        big integer 0

pga_aggregate_limit                  big integer 12G

pga_aggregate_target                 big integer 6G

Any idea?

Thanks in advance,

Regards,