Missing bundle for entity type bat_event

Problem/Motivation

I followed one of those video tutorials (Events | Drupal standard) and use Fullcalendar View module to create event calendars for displaying events created with BEE. It was working fine until I updated the Drupal core from version 9.2.16 to 9.3.9. After updating Drupal core, the calendar page shows "The website encountered an unexpected error. Please try again later". When I checked the "Recent log messages", I see PHP error "Drupal\Core\Entity\EntityStorageException: Missing bundle for entity type bat_event in Drupal\Core\Entity\ContentEntityStorageBase->doCreate() (line 125 of /home/booking/drupal/web/core/lib/Drupal/Core/Entity/ContentEntityStorageBase.php)."
Sorry I'm not sure where is the best place to post this bug report, since it also involves Fullcalendar View module, and BAT module. I hope maintainers of BEE module can point me to the right direction. Thanks.

Steps to reproduce

1. Install Drupal core 9.2.16, install BEE and Fullcalenar View modules.
2. Add a few reservations.
3. Create a view page to show "Event" of type "Availability Hourly", with display format "Full Calendar Display". Make sure BAT events can displayed properly.
4. Update Drupal core from 9.2.16 to 9.3.9.
5. revisit the view page.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes