Do pre-ping on pooled database connections

backend/app.py

@@ -62,6 +62,7 @@ app = Flask(__name__)
 
 app.config["SECRET_KEY"] = SECRET_KEY
 app.config["SQLALCHEMY_DATABASE_URI"] = SQLALCHEMY_DATABASE_URI
+app.config["SQLALCHEMY_ENGINE_OPTIONS"] = {'pool_pre_ping': True}
 app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = SQLALCHEMY_TRACK_MODIFICATIONS
 
 app.logger.setLevel(logging.INFO)