Flask restx Debug "Unauthorized" response

I have a Flask (2.2.3) app with Flask-RESTX (1.1.0) used as an API (without frontend). I'm using flask-azure-oauth library to authenticate users using Azure AD. The setup is:

from flask import Flask, current_app
from flask_azure_oauth import FlaskAzureOauth
from flask_restx import Api

app = Flask(__name__)
api = Api(app, <...>)
CORS(app)
auth = FlaskAzureOauth()
auth.init_app(app)

# App routes
@api.route("/foo")
class FooCollection(Resource):
    @auth('my_role')
    def get(self):
        return [<...>]

This was working fine, but since a few days I started to receive Unauthorized responses when passing valid token. Unfortunately I am not able to track the reason - tokens seem fine (examined manually or decoded using jwt.ms) and the only response I have from API is: 401 UNAUTHORIZED with response body { "message": null }.

I tried to add error logging and error handlers:

# Logging request/response
@app.before_request
def log_request_info():
    app.logger.debug(f"{request.method} {request.path} {request.data}")

@app.after_request
def log_response_info(response):
    app.logger.debug(f"{response.status}")
    return response

# Error handling
@app.errorhandler(Unauthorized)
def handle_error(error):
    current_app.logger.debug(f"Oops")
    <...>

@app.errorhandler
def handle_error(error):
    current_app.logger.debug(f"Noooo...!")
    <...>

With this, request and response are logged and non-HTTP exceptions are handled by handle_error. But HTTP errors like 404, 401, ... are just passing by, ignored by both generic error handler and a specific one (@app.errorhandler(Unauthorized)).

So how do I properly intercept and examine them? (with focus on: how do I find out why it denied token authorization)

from Flask restx Debug "Unauthorized" response