I am using the webforms module (6.1.1) on a Drupal 8 site for a form that shows up in a block on my front page.
If I am not logged in (go Incognito or InPrivate mode) the form displays and works.
If I am logged in, the form does not show, but the < div> it is located in does.
It works in the admin pages as expected.
I have verified that the Webform's Access has Roles "Anonymous user", "Authenticated user" and "Administrator" checked.
I have verified the Block also has Roles "Anonymous user", "Authenticated user" and "Administrator" checked.
Looking in the browser's developer view at the space where the form should be, I get the following code instead. I don't know if it is relevant or not.
This is opposite than most web hits that talk about the form not showing up for anonymous users.