Let's say something like this is being returned.

sqlalchemy.orm.exc.DetachedInstanceError: Instance <users at 0x1ff9aa91350> is not bound to a Session; attribute refresh operation cannot proceed (Background on this error at: https://sqlalche.me/e/14/bhk3)

In this example, "users" is a class, perhaps something like this.

from . import db

class users(db.Model):
  id        = db.Column(db.Integer, nullable=False, unique=True, primary_key=True)
  firstname = db.Column(db.String(20), nullable=False, unique=True)
  lastname  = db.Column(db.String(40), nullable=False, unique=False)
  state     = db.Column(db.String(10), nullable=False, unique=False)

Here is an example that would produce this issue. After session.close() there are print statements using data. The data object was "removed" by session.close().

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import func, exc

db = SQLAlchemy()

def app_obj():
    app = Flask(__name__)

    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
    app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = True
    app.config["SQLALCHEMY_ECHO"] = True
    app.config["SQLALCHEMY_RECORD_QUERIES"] = True

    db.init_app(app)

    with app.app_context():
        db.create_all()

        from .models import users

        data = users.query.filter_by(email='john.doe@example.com').first()

        print("before data.email     = " + str(data.email))
        print("before data.firstname = " + str(data.firstname))
        print("before data.lastname  = " + str(data.lastname))
        print("before data.state     = " + str(data.state))

        data.state = 'active'
        try:
            db.session.commit()
        except exc.SQLAlchemyError as sqlalchemyerror:
            print("got the following SQLAlchemyError: " + str(sqlalchemyerror))
        except Exception as exception:
            print("got the following Exception: " + str(exception))
        finally:
            db.session.close()

        print("after data.email     = " + str(data.email))
        print("after data.firstname = " + str(data.firstname))
        print("after data.lastname  = " + str(data.lastname))
        print("after data.state     = " + str(data.state))

    return app