My coworker is trying to access the Content Library in the Hub Site that I have been building to add data, but is signed out when he clicks on the Content Library tab. He's tried it in a few browsers but the problem still persists. The Hub Site is shared with him via a group (which we have used previously to share data and apps without issue).
We never figured out why this happens, but our work around was adding my coworker to the group that was created when I made the Hub site, which solved the issue.