Where? In former communist countries the workers didn't have any power after the seizing of the means of production, as now they were ruled by brutal dictatorships with powerful militaries who'd send you to the gulag for $REASON.
Hardly the envisioned "seizing the means of production" and more like "being seized for production".
Where would you see that evidence if it was nevere done? Because it can't really be done.
Because the workers themselves don't have power to seize anything. The military is the one with the power to seize stuff come a revolution because they're the ones with a lot of big guns, not the workers. But now the workers themselves become part of the things being seized, to serve the military leadership, not the workers.