Percona XtraDB Cluster (5.6.28-76.1-56-log) - random OOM events
Rate Per Second = RPS

Suggestions to consider for your AWS Parameters group

max_connections=300  # from 400 because max_used_connections was 197
innodb_flush_neighbors=2  # from 1 to reduce 95,455 innodb_buffer_pool_pages_dirty faster
innodb_io_capacity=900  # from 200 to use more of your IOPS available
read_buffer_size=262144  # from 2M to reduce handler_read_next RPS of 2,416,022
read_rnd_buffer_size=196608  # from 16M to reduce handler_read_rnd_next RPS of 965,300


to reduce MySQL RAM footprint and reduce CPU busy with performance improvement.

Please view my profile, Network profile for free downloadable Utility Scripts to improve performance and contact info.