As we got our freeze on the DedicatedServer + full map and gameplay classes, we tried going back to a simple empty level. That one doesn’t freeze, at least not for the past 2 hours.
We now try to add back the GameMode to that empty level, so nothing but the default skybox and one widget. If this freezes then I can at least cut out the map and its actors and reduce the search to the GameMode classes and the widgets.