TL;DR
Frozen entities currently do not have an Alert like e.g. entities missing material for construction do. Consider adding such an alert.Why?
Example use case: In Aquilo map view, I currently cannot tell at all when half my factory has frozen over.And from a more philosophical perspective, Factorio's Alerts feature feels like it should function a bit like an in-game issue tracker, so that a player could eliminate certain classes of errors in their factory by going through all alerts and fixing them. At least I assume that's the idea behind all the "missing construction material" alerts. A factory that's frozen over surely counts as a similar class of error.