We merged the following pull requests which should address this issue:
Initially, we had planned to allow read-only users to preview chat channels, but designing the user experience for that turned out to be a bit more complicated than we originally anticipated, so we removed that feature for now in the name of simplicity.
Note: if you had channels set up with auto-join that included groups with read-only permissions, you may need to edit the channel settings once to force the membership list to synchronize with these new rules.