BUG #18966: Invalid SQL queries hang indefinitely until server restart

The following bug has been logged on the website:

Bug reference: 18966
Logged by: Jérémy S
Email address: jeremy(dot)spriet(at)gmail(dot)com
PostgreSQL version: 16.9
Operating system: Docker debian
Description:

Hello,
I’m running PostgreSQL 16.9 in Docker (PostgreSQL 16.9 (Debian
16.9-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc 12.2.0, 64-bit),
and intermittently observe that invalid SQL queries hang indefinitely
instead of immediately returning an error.
Valid queries continue to work normally and return results right away.
I usually issue statements via a Python client library, but when the issue
occurs, I see the same blocking behavior connecting directly with psql—the
session simply stalls and never reports syntax errors, “relation does not
exist,” or any other error.
Only a full restart of the Docker container unblocks all sessions.
This has happened 2–3 times over the past six months, but I haven’t been
able to reproduce it on demand.
When a query hangs, even running: SELECT pg_cancel_backend(pid); or SELECT
pg_terminate_backend(pid); does not unblock it. Only restarting the
container helps.
Does anyone have ideas on what could be causing this behavior?
My postgresql.conf:
listen_addresses = '*'
max_prepared_transactions = 0
shared_buffers = 2000MB
temp_buffers = 8MB
max_connections = 5010
superuser_reserved_connections = 2
shared_preload_libraries = 'timescaledb,pg_cron,pg_stat_statements'
cron.database_name = 'db1'
pg_stat_statements.max = 5000
pg_stat_statements.track = top
Thanks!