I was in South Quel Woods. I set the 4 decaying scarecrows on fire and I fought a couple of large spiders.... No scarecrow. I was in a party with 1 other player while doing that.
i just checked it. it worked fine. check that none of the wave mobs wandered off to attack other scene mobs.
I went there yesterday agaain and was able to summon it twice while being in the zone, so it´s working fine. The high wheat? in the field makes it a bit difficult to notice if one of those many spiders wanders off to attack something else closeby.