LinkedIn oAuth failing to redirect for some users - 1x1 pixel returned

We're seeing a handful of users who are unable to complete the LinkedIn oAuth authorisation flow in their browser, though it works fine for hundreds of other users (and in our own dev tests).

Our code redirects to this URL as per the documentation:

https://www.linkedin.com/uas/oauth2/authorization?response_type=code&client_id=xxxxxxxx&scope=r_basicprofile%20rw_company_admin%20r_emailaddress%20w_share&state=xxxxxxx.xxxxxxx&redirect_uri=https%3A%2F%2Fdomain.com%2Flinkedin_oauth%2Fcompany

When working correctly, it 302 redirects back to our domain with a code parameter.

However, for a few users, it just returns a 1x1 pixel instead of the 302 redirect.

Given the oAuth flow should always allow a user to fix any problems, or for our app to report an error message, this looks like a bug.