I was playing gambit with a fireteam through matchmaking. We were up by 98-60 (approximately) and then suddenly the enemies stopped spawning. We searched the whole map, but no enemies spawned anywhere. The enemy team on the other hand gradually collected their motes and summoned the primeval. Luckily, one enemy spawned with "white aura" and when we killed it, it gave us 5 motes and we were finally able to summon the primeval. Some other people also faced the issue few days ago, saw it in the forum.
Devs should take a look