Since D11827 we have an "import" heuristic which triggers on pushes to hosted repositories: if you push more than 7 commits to an imported, empty repository, we kick it back into importing mode.

This heuristic does not activate for imported repositories because we don't know where the boundaries of pushes are.

We could at least try to do the same thing with imported repositories, although it is less reliable and somewhat race-prone: if we discover more than 7 commits in an imported, empty repository, kick it back into importing mode. It's possible that the parsers will get ahead of discovery and we'll lose the mode before import finishes, but this should be a difficult race for the discovery daemon to lose since the import daemons need to jump through so many steps.