2021-11-05 14:35:09.197 UTC [1451469] LOG: received smart shutdown request
2021-11-05 14:35:09.222 UTC [1451660] postgres@breedbase FATAL: terminating connection due to administrator command
That does not look like PostgreSQL crashed but is being shutdown by RDS services due to a DOS attack.
Two things;
1. A firewall should be blocking the incoming rouge traffic to protect the given server; otherwise the system is open to a DOS attack.
2. Why is PostgreSQL accessible on the internet? Normally DB servers are at least 3 deep from the internet and only internal trusted nodes should be connecting to the database.