This map should be ideal for sniper gaunlet with a lot of open spaces. During two runs (one with Preacher, one with Veteran) , I experienced lower level of “excitement” than on other maps with this modifier. In both cases only two or three waves were spawned.
During the second game, using Veteran X-Ray vision, I noticed multiple Snipers prepared behind spawn doors but not entering combat.
During finale, I counted at least eight snipers in far-away locations. Also we had to wait around five minutes to leave the map - maybe game was expecting us to eliminate them.
By the way, I like this modifier. 
I think it’s mostly the AI director. Sometimes they don’t let up, other times it can feel a bit light.
I noticed on one run a group of them got stuck and couldn’t get into position to attack us during an event. We ended up moving away from them and it was awhile before a new group spawned in. Might be related to low number of sniper spawns.
Just ran into the same bug on Consignment Yard, we waited for about 10 minutes and gave up and quit. We could see the snipers who got stuck way back earlier on the map with Vet ability, but couldn’t kill them and the event wouldn’t end. GG FS
Just did this on Consignment Yard. It wasn’t the snipers stuck in another room. It was actually a random enemy somewhere in the arena that didn’t aggro onto us and we spent a good few minutes scouring the area and eventually found them on accident.
I believe the event only counts for enemies currently spawned inside the area during the timed phase of the objective and therefor doesn’t count anything outside of it, even if they do spawn in and enter the arena after the event changes the objective.
I’ve seen something similar in Smelter Complex. A group of snipers stuck at spawn point near the door it seems, they were chilling afk like roamers but they also weren’t reacting on shots at them.
Today I played this map and modifier twice. Experience was much better - after sound warnings there was always a squad of sniper in waiting. Sometimes they lurked big rooms, sometimes they blocked corridors.
Once there was sound warning just before finale but only two snipers appeared and not as a group. I susped sniper groups are not allowed for the final fight.
Epic finale with galleries full of snipers might be an epic finale (maybe combined with gunners).
And yet again I played this map/mode - on Heresy…
And it was Brutal!
The mix of map enemies, hordes and Snipers was intense.
We barely got to the room with the last MedStation because door was protected by a pair of snipers and grenadier. We had to use usually unnecessary thing called group tactics 
to close door to revive a mate then throw flashbang and rush into room.
In the “open the door” semi-finale, we were ambushed by two snipers from next map section. The were shooting trough some narrow passages while we were activating top terminals.
The finale felt like mixed Sniper gauntlet + Specials gauntlet. Actually the whole game felt like mixed.
Again, we faced delayed finish as after clearing the trainyard, we had to eliminate two more special waves.