Why is "skipping missing configuration file" repeatedly appearing in Aurora PostgreSQL logs after upgrading from 11 to 16?

After upgrading an Aurora PostgreSQL cluster from 11.21 to 16.1 using a blue-green deployment, we're seeing a bunch of log statements that don't make sense.

For example, after rebooting the writer instance, we see:

2024-02-14 19:12:37.392 GMT [542] LOG: skipping missing configuration file "/rdsdbdata/config/recovery.conf"
2024-02-14 19:12:37.393 GMT [542] LOG: skipping missing configuration file "/rdsdbdata/config/recovery.conf"
2024-02-14 19:12:37.393 GMT [542] LOG: skipping missing configuration file "/rdsdbdata/db/postgresql.auto.conf"
2024-02-14 19:12:37 UTC::@:[542]:WARNING: invalid configuration parameter name "rds.babelfish_status", removing it
2024-02-14 19:12:37 UTC::@:[542]:DETAIL: "rds" is now a reserved prefix.
2024-02-14 19:12:37 UTC::@:[542]:WARNING: invalid configuration parameter name "rds.adaptive_autovacuum", removing it
2024-02-14 19:12:37 UTC::@:[542]:DETAIL: "rds" is now a reserved prefix.
2024-02-14 19:12:37 UTC::@:[542]:WARNING: invalid configuration parameter name "rds.csd_test_parameter_3", removing it
2024-02-14 19:12:37 UTC::@:[542]:DETAIL: "rds" is now a reserved prefix.
2024-02-14 19:12:37 UTC::@:[542]:WARNING: invalid configuration parameter name "rds.enable_plan_management", removing it
2024-02-14 19:12:37 UTC::@:[542]:DETAIL: "rds" is now a reserved prefix.
2024-02-14 19:12:37 UTC::@:[542]:LOG: redirecting log output to logging collector process
2024-02-14 19:12:37 UTC::@:[542]:HINT: Future log output will appear in directory "/rdsdbdata/log/error".

We're observing no other symptoms of a problem. Everything appears to be working well.

The ones that seems most concerning are the "skipping missing configuration file" messages. Are these anything to be concerned about?

I know the parameter groups are working. I've changed parameters in the group, and the expected values appear via SHOW ALL in psql.