This map is very complex, 1228 triggers, just shy of 20k lines in trigedit text. I've never seen this particular bug before after playing probably over a hundred games of various versions of this map, but I've now seen it twice in 3 games.
In DS, units spawn for each team at the bottom left or top right of the map. In my version, the bottom CPU is player 4 and is teal coloured, and the top CPU is player 8 and is tan coloured (identical to P11 colours). Units are initially spawned in holding pens and then moved to the field when room permits, to prevent unplacable unit errors and ensure that your army fully spawns. There are several triggers that govern this behaviour (since it's timed, and the units spawn for P1-3 and must be given to P4 for example), but the one that finally moves units onto the filed for each player, moves the units and then has an Order action like this:
Issue order to all [men] owned by [Current Player] at [move to field mine]: [patrol] to [temple target enemy]
This trigger is owned by Force 2, which contains CPU players 4 and 8.
There is another set of triggers that periodically (every 15 seconds or so) re-issues orders to all CPU units on the map to attack towards the enemy temple, because CPU units can sometimes get lost or lose their targets and sit around doing nothing. There are actually multiple actions for each specific type of unit, because some units are ordered to Move or Attack instead of Patrol, and air units are triggered in a different interval to ground units, but in general they all look like this:
Issue order to all [men] owned by [Current Player] at [My side of map || enemy side of map]: [patrol || move || attack] to [temple target enemy]
Now the actual bug that happened is that suddenly, all of the units owned by Player 4 on the battlefield (probably about 80+) stopped moving - they all just stood still in their tracks. The periodic attack timers did nothing. There was a big big group of protoss units sitting in the [move to field mine] location not moving at all, even though they should have immediately been given the order to patrol. The really odd thing is that the next player, who was zerg, had their spawn turn, and so there was then a big swag of zerg units sitting in the spawning pens. Very very slowly, these zerg units were moved to the field around the protoss units, as evidently there was a smidge of room for them to be placed. As soon as the zerg units arrived, they began patrolling towards the enemy temple, like they should, but all of the protoss units simply stood there motionless.
The obvious explanation for this is that the order triggers were now not firing for those protoss units that were frozen, neither the periodic ones or the single order to patrol when they are first moved to the field, that also fired when the zerg units moved to the field. This would easily happen if the units were no longer owned by Player 4, but were owned instead by any other player. However the units were still Teal on the main screen, and Teal on the minimap. If they had been given to P1-3, P4-8 they would have changed colour on the field and the minimap, and if they were given to P9-12 they would remain Teal on the main screen but turned a different colour in the minimap. And this specifically did not happen.
This motionless non-order state stayed in place for 2 or 3 spawn cycles, during which new units were moved to the field and patrolled correctly, but the protoss units sat in a big lump not moving - other units further out in the field were quickly massacred by the P8 CPU units. Interestingly, these units did not fight back in any way at all, so it seems like it wasn't just a lack of orders, but a complete lack of any action at all that suddenly afflicted these units - I'm not even sure if they were doing their normal idle animations where they slowly rotate around and face different directions.
Eventually a player on the P1-3 team (my team) used the zerg Infestation special. Suddenly all of the protoss units began moving again, as they were supposed to. The infestation special does end with an order trigger:
Issue order to all [men] owned by [Current Player] at [anywhere]: [patrol] to [temple target: enemy]
So it seems that this order action was properly executed for the protoss units, whereas the other periodic ones were not?
Now this happened again, although much more briefly, in my 3rd game. Except this time it was the P8 zerg units (my enemy) that froze, and it was only a few of them. They stayed frozen for about 30-40 seconds, and came right all by themselves - there was no special, or boom, or any other special event that happened. Again, they remained Tan colour both on the main screen and on the minimap. I made a test version of my map to see what happened when players were given to P11, who is also tan - in that case the Photon Cannons at the top team base begin firing on the units, as they are now considered enemies. In this game with the zerg units, several of them froze right next to the photon cannons, but the cannons did not attack them, so this is a strong sign that they were not given to player 11 inadvertently.
Does anyone have any clues what might be going wrong? I think I can rule out the units being given to another player in error because the unit & minimap colours didn't change. I think I can also rule out the locations being incorrectly moved around, because in the first game the zerg units were still being correctly moved to the field and correctly ordered to patrol, and the periodic triggers have locations that cover the entire field and should not be being moved by any other triggers. However it is a bit suspicious that the order for men in [anywhere] at the end of the Infestation special did make the protoss units move. But in the 3rd game, there wasn't any special event that happened, the units just seemed to 'snap out of it' after a while.
None.