Set queue size = 1 to Copy island right after the desync.
In this case, Copy won't read more data from a "last_written"
container than required, while feeding the desynchronized path.
Sometimes Copy don't get fused into an island and behaves
on its own -- in this case, it reads more data in advance
so the slow (desync) part actually processes some data in-sync
(more than actually required)
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