Azure App Service is a service used to create and deploy scalable, mission-critical web apps.
@Suresh G Nair Thanks for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this.
I am summarizing the above and posting the same as Answer for the benefit of community.
Post adding the app setting WEBSITES_CONTAINER_START_TIME_LIMIT with value 1800 from backend logs we see that container is up and able to accept the requests.
If are still facing any issue like application error while requesting the root(/) of your app service I would suggest you enable diagnostic logging and review the application logs or use the webapp Down detector under Diagnose and solve problems to troubleshoot or understand more about these issues. I hope the answer helps. Please let me know if you have any further queries.
Please accept as Yes if the answer provided is useful, so that you can help others in the community looking for remediation for similar issues.