LogDevice clients do notify sequencers if they have seen newer epochs, which would cause a sequencer reactivation, which indeed resolves the issue within the context of a single client.

However, there can still be reordering in the context of a wider system. E.g. if client A sends a write (w1) to sequencer in epoch X, which gets replicated and acknowledged, and after that client B sends a write (w2) to sequencer in epoch (X-1) which gets replicated and acknowledged (because epoch X-1 is not sealed), then readers eventually will see w2 before w1. If writes in epoch X weren't accepted before the sealing of the epoch (X-1) had completed, this reordering would be impossible, however as a result write availability would suffer.