The Changelog (v 0.110) says

"Crusader enemies in the "Echoes" objective will no longer block spawns"

atm... im playing "The Lost World" objective. and i think there is an issue, too.
when there is one or more of the "special skilled dinosaurs" on the screen, the spawn speed is decreased :/
when the tank enemies finally get killed, the spawn speed is normal again...
aaaaaaaand there is the next tank dino :/

its very very slow... spawn speed buffs have no effect if there is a tank enemy on the screen
pretty much the same as the "Echoes" objective before it got fixed...
http://forum.codenameentertainment.com/?thread_id=13833

and the collect 1 areas are very difficult if there are no spawns when there is a tank on the screen because of the asteroids (insta-kill)