pgAdmin4 and AWS ALB + WAF: AttributeError: 'NoneType' object has no attribute '_query'

Context: pgadmin4 (any recent version) is deployed as a pod in AWS EKS and accessed via public ALB + WAF with public HTTPS certs. BD: AWS RDS in the same VPC. Pgadmin mostly works fine, but some queries give the next error:

Traceback (most recent call last):
  File "/venv/lib/python3.11/site-packages/flask/app.py", line 1484, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "/venv/lib/python3.11/site-packages/flask/app.py", line 1469, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/venv/lib/python3.11/site-packages/flask_login/utils.py", line 290, in decorated_view
    return current_app.ensure_sync(func)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/pgadmin4/pgadmin/tools/sqleditor/__init__.py", line 979, in poll
    conn._Connection__async_cursor._query)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute '_query'

The most interesting part: all queries work good if I open pgadmin not via ALB but via port forwarding from the pod or k8s service directly (without ALB).

Solution

AWS WAF (assigned on my ALB) blocked some queries because of AWS#AWSManagedRulesSQLiRuleSet#SQLi_BODY rule in AWS-AWSManagedRulesSQLiRuleSet. I realised it when I saw "forbidden" errors in browser developer console.