Hey Alex,
Welcome back and sorry to see you’re experiencing troubles. I see you checked ‘Yes’ to reverting back to the default WordPress theme and deactivating all plugins other than ours as instructed in the Testing for conflicts guide, but can you please confirm this?
I went ahead and attempted to reproduce the missing attendee info, but as you can see in the screenshot below, the information is displaying for me:

Can you send your System Information as a private reply? It would also be helpful if you could test once more, but this time please make sure WP_DEBUG and WP_DEBUG_LOG are enabled on your site’s wp-config.php file. Any errors will display at the top of your page as you try to reproduce the conflict. Note what you find and please include it in your reply.
Thanks and have a good rest of your day. Cheers!