Dear Ben,
I found the problem. In Types, when you run a types_render_field, it will try to establish the post_id of currently edited post via get_the_ID(). But, as you may know, a post doesn't have an ID until it gets saved into the database, at least as a draft. If you check, this notice doesn't appear once you save the Venue as a draft.
It's not an error, though, so silencing it with @ is one of the options. I would suggest you to change the functionality a little to not to display any fields before the post ID is available. It's actually not a Toolset thing, it's related to how WordPress works, so we can't create a workaround for this.
I'll talk to our developers and suggest a bit of code to have it silenced in the future.
Please let me know if you are satisfied with my answer and if I can help you with any other questions you might have.
Regards,
Paweł