Hello,
I’m sorry that the ticket form isn’t showing up correctly, but I’ll be happy to help you out with this.
First, you can try adjusting the “Default stylesheet used for events templates” and “Events template” settings under Events > Settings > Display. These affect how much events pages inherit their styling from the theme (theme conflicts are a common cause of these types of issues with the ticket form buttons).
It looks like you have already tried switching to a default environment with all other plugins besides The Events Calendar, Event Tickets, and Event Tickets Plus disabled, and a default theme like Twenty Seventeen enabled and were still seeing this issue, is that correct? If you haven’t switched to a completely default environment already, you’ll want to start there. You can use the free Duplicator plugin to create a staging environment if you don’t have already. From there, you can re-enable things one at a time (as described here) to see if you can find any conflicts – I would recommend starting with your theme.
If you don’t find any conflicts, can you please send me your full system info plus a link to this page directly so that I can take a look?
Thanks,
Jennifer