Performance issues from RDS Aurora 5.6 to Aurora 5.7
Rate Per Second = RPS
Suggestions to consider for your 5.7.12 Aurora Parameters group
innodb_write_io_threads=16  # from 4 to enable higher IOPS to your SSD device
innodb_lru_scan_depth=100  # from 1024 to conserve 90% of CPU cycles used for function
innodb_max_dirty_pages_pct_lwm=.0001  # from 0 to enable pre-flushing
innodb_max_dirty_pages_pct=.0001  # from 75 % dirty tolerated to reduce innodb_buffer_pool_pages_dirty count of 354,764 - will take hours
net_buffer_length=98304  # from 16384 to reduce count of interruptions for send/receive pkts
innodb_fast_shutdown=0  # from 1 to avoid recovery cycle on restart

This is just the beginning of your journey to improve performance.
Thank you for the opportunity to serve your team.
Not all these Global Variables are dynamic.  Will require instance stop/start.