How to fix Cache lookup failed for function in PostgreSQL

DROP FUNCTION my_function(int);
CREATE FUNCTION my_function(int) RETURNS text AS $$
  BEGIN
    RETURN 'updated';
  END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION my_function(int) RETURNS text AS $$
  BEGIN
    RETURN 'updated';
  END;
$$ LANGUAGE plpgsql;

-- Find sessions using the function's schema
SELECT pid, usename, state FROM pg_stat_activity WHERE state != 'idle';

-- Terminate specific sessions
SELECT pg_terminate_backend(pid) FROM pg_stat_activity 
WHERE usename = 'app_user' AND state != 'idle';

-- Find the function
SELECT oid, proname, pronamespace, pronargs 
FROM pg_proc 
WHERE proname = 'my_function';

-- Check function signature
SELECT pg_get_functiondef('my_function(int)'::regprocedure);

-- List all functions in a schema
SELECT p.proname, pg_get_functiondef(p.oid)
FROM pg_proc p
JOIN pg_namespace n ON p.pronamespace = n.oid
WHERE n.nspname = 'public';

# Stop PostgreSQL
sudo systemctl stop postgresql

# Run in single-user mode
sudo -u postgres /usr/lib/postgresql/[VERSION]/bin/postgres -D /var/lib/postgresql/[VERSION]/main --single

REINDEX INDEX pg_proc_oid_index;
REINDEX INDEX pg_proc_proname_nsp_index;

-- View the function source code
SELECT prosrc FROM pg_proc WHERE proname = 'my_function';

-- List function dependencies
SELECT DISTINCT dependent.proname as depending_function,
       dependency.proname as called_function
FROM pg_depend
JOIN pg_proc dependent ON pg_depend.refobjid = dependent.oid
JOIN pg_proc dependency ON pg_depend.objid = dependency.oid
WHERE pg_depend.objid IN (
  SELECT oid FROM pg_proc WHERE proname = 'my_function'
);

CREATE OR REPLACE FUNCTION my_function(int) RETURNS text AS $$ ... $$ LANGUAGE plpgsql;

-- Keep old function as wrapper
CREATE OR REPLACE FUNCTION my_function(int) RETURNS text AS $$
  SELECT my_function_v2($1);
$$ LANGUAGE sql;

-- Create new implementation
CREATE FUNCTION my_function_v2(int) RETURNS text AS $$ ... $$ LANGUAGE plpgsql;

BEGIN;
DROP FUNCTION IF EXISTS my_function(int);
CREATE FUNCTION my_function(int) RETURNS text AS $$ ... $$ LANGUAGE plpgsql;
COMMIT;

-- Then force all clients to reconnect