Responding to a post from over 10 years ago, but: the issue in the above post is probably move order.
If the snake moves before the roach queens, then it has to move to block the spawning spaces during turn 30.
If the roach moves after the roach queens, then it has to already be blocking those spaces before turn 30 starts.
So it's likely that during the testing, the move order was changed and therefore a position worked in some tests and not in others.
In the room itself, the snake moves first; this means it has to be moving counterclockwise in order to block the spawn, as its head will always be on a white square whenever the queens attempt to spawn.
For anyone struggling to get the snake over there:
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×Move it in a loop until its head is on (25,2) on turn 12.
As to how to get rid of it:
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×Hit the orb that toggles the door in the loop, just as the snake's head is on it. Then you can run around and get north of the queens by the time they spawn.