Try changing them to:

db_block_buffers = 40000
db_block_lru_latches = 12

Do you use keep or recycle pool? Like:

buffer_pool_keep = (buffers:5000, lru_latches:2)
buffer_pool_recycle = (buffers: 10000, lru_latches:2)

I would recommend setting a recycle pool in init.ora to something only if you know and understand why you are doing that!