Slack pulse certain users receiving broken images

When sending pulses via Slack as a direct message, some users are receiving broken images instead of a pulse graph. The same pulse can be seen by others, via DM. Example images are below.

^^ broken image

^^ same pulse to different users

Does these users have access to the metabase_files channel?

We had problems that some users could not see the images, but if was because they hadn’t got access to metabase_files.