Configuring how Slack workspaces are grouped?

I've recently upgraded my mautrix-slack bridge to 0.1.4, and it seems to be inconsistent how Slack workspaces are grouped client-side, see screenshot:  Some older workspaces are grouped under "Slack", while the recently added "F-Klubben" workspace is separate. I have not found any way to configure this in the yaml file; when I leave and re-login to one of the older spaces, it gets re-added under "Slack". How can I ungroup them?