Well there are a lot of things processing, espacially if you have Availability Check. And it can become quite long if you have a lot of orders or products.
Try to go to Easy Booking > Settings > Booking Statuses and save (don’t change your settings, just save). Then init availabilities in Easy Booking > Availability Check. I can’t guarantee it will improve things but you can try.
Can you try disabling Easy Booking and/or Availability Check to make sure it’s causing the issue? Otherwise it can be a server issue.