Hi,
I can help troubleshoot them.
Can you please confirm you are using Eventbrite Tickets 3.9.6 and that you have followed the configuration steps outlined here:
https://theeventscalendar.com/knowledgebase/configuring-eb-tickets/
Then can you go to an event that is suppose to show the tickets box and confirm this setting in the admin for that event is set to yes:
Display tickets on event page?
Even if it is set to yes can you please set it to no, then update, and then set back to yes and update again and see if it shows.
Let me know what you find out and we can go from there.
Thanks