Hey All,
As mentioned above, we’re not able to consistently reproduce this as a bug. Sharing a prototype without having to log in is working as expected on our end.
Again, if all of your share settings are correct, please send a file link directly to our support team via this form for help: https://help.figma.com/hc/en-us/requests/new
Be sure to use your Figma account email and share it with support-share@figma.com, so we can take a closer look.